Of all the elements in a PC, few are as overlooked and ignored as the battery. Batteries play an important role in all PCs by maintaining the system's configuration data while main AC power is turned off (just imagine how inconvenient it would be to re-enter the entire system setup in CMOS before being able to use the system each time). For portable systems such as notebook and sub-notebook PCs, battery packs also provide main power for the entire system. This chapter outlines the technologies and operating characteristics of today's battery families, and illustrates a selection of battery-related problems that can plague a PC.

The battery is perhaps the most common and dependable source of power ever developed. It is an electrochemical device which uses two dissimilar metals (called electrodes) that are immersed or encapsulated in a chemical catalyst (or electrolyte). The chemical reaction that takes place in a battery causes a voltage differential to be developed across its electrodes. When a battery is attached to a circuit, the battery provides current. The more current required by a load, the faster a chemical reaction will occur. As the chemical reaction continues, electrodes are consumed. As a result of this chemical consumption, the battery will eventually wear out. It is important to realize that a battery and a cell are not necessarily the same. A cell is the basic element of a battery, however, a battery may be made up of several individual cells.

For some batteries, the chemical reaction is irreversible. When the battery is dead, it must be discarded. These are known as non-rechargeable (or primary) batteries. Most PCs use primary-type batteries to sustain the CMOS Setup. However, some types of batteries CAN be recharged. By applying current to the battery from an external source (i.e. a battery charger), the expended chemical reaction can be almost entirely reversed. Such rechargeable batteries are referred to as secondary batteries. Secondary batteries are used to supply main power for all mobile computers.

Batteries carry two important ratings; cell voltage and ampere-hours (Ah). Cell voltage refers to the cell's working voltage. Most everyday cells operate around +1.5 Vdc, but can range from +1.2 to +3.0 Vdc depending on the particular battery chemistry in use. The ampere-hour rating is a bit more involved, but it reflects the "energy storage capacity" of a battery. A large Ah rating suggests a high-capacity battery, and vice versa.

As an example, suppose your battery is rated for 2 Ah. Ideally, you should be able to draw 2 amps from the battery for 1 hour before it is exhausted. However, you should also be able to draw 1 amp for 2 hours, 0.5 amps for 4 hours, 0.1 amps for 20 hours, and so on. Keep in mind that the ampere-hour relationship is not always precisely linear. Higher current loads may shorten battery life to less than that expected by the ampere-hour rating, while small loads may allow slightly more battery life than expected. Regardless of the ampere-hour rating, all batteries have an upper current limit - attempting to draw excess current can destroy the battery. Physically large batteries can usually supply more current (and last longer) than smaller batteries. Another way to express a battery's energy capacity is in Watt-hours per kilogram (Wh/kg) or Watt-hours per pound (Wh/lb). For example, a 1 kg battery rated at 60 Wh could provide 60 W of power for 1 hour, 30 W of power for 2 hours, 10 W of power for 6 hours, etc.

In its simplest sense, charging is the replacement of electrical energy to batteries whose stored chemical energy has been discharged. By applying an electrical current to a discharged battery over a given period of time, it is possible to cause a chemical recombination at the battery's electrodes which will restore most of the cell's spent potential. Essentially, you must back-feed the battery at a known, controlled rate.

NOTE: Recharging only works for secondary cells such as nickel-cadmium or nickel metal-hydride batteries. Attempting to recharge a primary battery will quickly destroy it.

Before you dive into an overview of charging circuits and troubleshooting, you must understand the concept of C. The term "C" designates the normal current capacity of a battery (in amperes). In most circumstances, the value of C is the same as the ampere-hour current level. For example, a battery rated for 1,300 mAh (1.30 Ah) would be considered to have a C value of 1.30 amps. A battery rated for 700 mAh (0.70 Ah) would have a C of 0.70 amps. Charging rates are based upon fractions or multiples of C.

To charge a battery, you must apply a reverse voltage which will cause the appropriate amount of charging current to flow back into the battery. Ideally, the battery should be charged at a rate of 0.1C. For batteries with a C of 500 mA (0.5 A), 0.1C would be 50 mA (0.05 A). At 0.1C, the battery could be left connected in the charger indefinitely without damage. Low-current charge rates such as 0.1C are sometimes referred to as a slow charge or trickle charge. Slow charging produces the least physical or thermal stress within a battery, and ensures the maximum possible number of charge/discharge cycles.

Many current secondary batteries can be charged well above the 0.1C rate. The quick charge approach uses current levels of 0.3C (three times the rate of a slow charge) to recharge the cell in 4 to 6 hours. For a battery with a C of 600 mA (0.60 A), the 0.1C charging rate would be 60 mA (0.06 A), but the quick charge rate would be 180 mA (0.18 A). However, the quick charging process runs the risk of overcharging a battery. Once a battery is fully recharged, additional current at or above the quick charge rate causes temperature and pressure buildups within the cell. In extreme cases, a severely overcharged cell may rupture and be destroyed. When quick charging, the 0.3C charging rate should be used only long enough to restore the bulk of a cell's energy. The rate should be reduced to 0.1C (or less) for continuous operation

New NiCd and NiMH battery designs allow for an even faster charge of 1 hour. The 1-hour charge uses a rate of 1.5C - 1.5 times the amount current which the cell is intended to provide. A battery with a C of 1,400 mA (1.40 A) would use a 1-hour charge rate of 2,100 mA (2.10 A). Remember that only specially-designed secondary cells can be safely charged in 1 hour or less. With 1-hour charging, current control and timing become critical issues. The battery charging current MUST be reduced as soon as the cell approaches its full charge, or catastrophic battery failure will almost certainly result. Rapid charging causes substantial temperature and pressure increases that eventually take their toll on a cell's working life. You should expect the working life of any cell to be curtailed when it is regularly operated in a 1-hour charge mode.

The constant-current charger is designed to automatically compensate for changes in battery terminal voltage in order to maintain charging current at a constant level. Constant-current charging is very efficient, but it is not adjustable. If the charger were set to deliver substantial charging currents, the battery pack could charge quickly, but the pack could eventually be damaged by overcharging. The charger could be set to a lower level for safe charging (perhaps 0.1C), but the low charging rate means very long charge times for a battery pack (10 hours or more). Such limitations make constant-current chargers ill-suited for use in mobile computers. Instead, constant-current chargers are typically used in stand-alone battery pack charging units.

A more effective approach for portable computers is a variable-current (constant-voltage) scheme. When a battery is deeply discharged and its terminal voltage is low, there will be a substantial difference between the power supply source and battery voltage level. This difference results in a sizable current flow to the battery. Charging usually starts out around the 0.5C to 0.3C rate for fast charge operation. As the battery takes on a charge, its terminal voltage increases. Higher battery voltage reduces the difference between the supply and battery - current flow into the battery decreases. When the battery pack reaches full charge, there is almost no voltage difference between the charger and battery, so only a small amount of current trickles into the battery. Current flow may reach levels as low as 0.05C.

When IBM released its PC/AT in the early 1980s, one of the many design changes over the older PC/XT was the elimination of DIP switches used to set the system configuration. Instead of discrete physical switches, PC designers chose to set system parameters using bit sequences stored in small areas of low-power static RAM. Since it would be necessary to maintain the contents of this RAM even when system power is off, designers choose to use RAM ICs based on Complementary Metal Oxide Semiconductor (or CMOS) fabrication. This memory became known as CMOS RAM. CMOS RAM can be maintained for years using only a single small battery or battery pack incorporated onto the motherboard (Fig. 8-1) called a CMOS backup battery.

Mobile computers such as IBM’s ThinkPad series often employ additional batteries to serve as a "standby" power source. These standby batteries are rechargeable battery packs frequently used to supplement the main battery in mobile computers. Traditionally, you’d need to shut down a laptop and replace a main battery pack, then reboot the system in order to keep working. If the main battery pack failed, you’d loose any work in progress (and perhaps corrupt important files). With a standby power source, the system can automatically enter a "suspend" mode where almost no power is used, but files and data can be kept active in memory. You can then replace the main battery and leave the "suspend" mode to keep working without the time and trouble to reboot and reload your applications. If the main battery should fail, the standby batteries can keep your work intact for up to several days until you can exchange the main battery pack, or find an AC outlet for a battery eliminator.

Lithium/manganese-dioxide (Li/MnO2 or simply "lithium") batteries are commonly employed as CMOS backup batteries. Lithium batteries use a layer of lithium as the anode, a specially formulated manganese-dioxide alloy as the cathode, and a conductive organic electrolyte. Depending on the overall size and shape of the cell, a lithium battery can supply +3.0 Vdc at up to 330 Wh/kg of energy density. Lithium cells also offer a 5 year shelf life with almost no loss of power. While their energy density is quite high, lithium cells offer only low ampere-hour ratings between 70 mAh (0.70 Ah) and 1,300 mAh (1.30 Ah). Limited Ah ratings allow lithium cells to maintain an almost constant output voltage over a long working life.

The classical type of lithium "coin cell" design is shown in Fig. 8-2. The typical coin cell is designed in two halves with a lithium anode at the top, and a manganese-dioxide cathode layer on the bottom. Both halves are separated by a thin membrane containing a conductive electrolyte. The finished electrochemical assembly is then packaged into a small metal can. The lid forms the negative electrode, while the side walls and bottom of the coin form the positive electrode. The lid is physically isolated from the rest of the metal can by a thin insulating grommet - thus, the coin cell is not sealed. A grommet keeps moisture and contaminants out, yet will allow any pressure buildup to escape the battery.

Battery life has a finite limit. Eventually, all backup batteries will discharge to the point where they can no longer sustain the system. When the battery finally does fail, CMOS information is lost. The next time you attempt to turn the PC on, the system will generate an error code or message indicating that the system configuration does not match the CMOS setup information. The loss of a CMOS setup suddenly leaves a system disabled until new (and correct) CMOS information is entered. This presents a serious problem for most PC users, since few users bother to backup or record their CMOS setup. As you might imagine, it then becomes an exercise in frustration to load the setup routine and re-construct the system setup from scratch.

Fortunately, there are two things you can do to avoid this problem. First, make it a point to replace the backup battery every 2 years (no more than 3 years). If you change the backup battery for a customer, note the battery part number and replacement date on a sticker, then place the sticker inside the PC enclosure. You might also note the next replacement date on your customer's bill. Second, backup the system CMOS entries before replacing the battery. You can note the entries on paper (using the form included in the appendix of this book) and tape the page inside the enclosure, or you can use a shareware utility to backup CMOS contents as a disk file. CMOS backup as a disk file is quick and easy, and the file can be restored in a matter of seconds. A backup utility is especially handy when there is no SETUP disk available for the system being worked on. Make it a point to keep the backup current as system parameters change. Otherwise, you would be restoring information that is no longer valid.

Companion CD: There are a number of CMOS backup/restore utilities for you to choose from. Check out CMOS.ZIP, CMOSRAM2.ZIP, AUTOCMOS.ZIP, and CMOS93CD.ZIP on the Companion CD.

The actual process of backup battery replacement is simply a matter or removing the old battery and inserting a new one. Since the battery is often located prominently on the motherboard, it is possible to replace a backup battery with system power applied (this lets the system maintain its CMOS settings). However, working inside a "hot" system is against the safety protocols that we have established for this book, so be sure to record the CMOS settings on floppy disk or paper first, then power down and unplug the PC before opening it. Replace the battery, then restart the PC and reload the CMOS settings from disk or paper. Replacing the backup battery in a notebook or sub-notebook PC is sometimes easier since the battery is usually accessible from a small panel on the bottom enclosure (you do not have to disassemble the notebook enclosures to replace the battery). Even with easy access, you should make it a point to remove power before replacing the battery.

NOTE: If you act quickly when replacing the CMOS backup battery, there may be enough of a latent charge in CMOS RAM where the contents will remain intact for several minutes. However, each motherboard is designed differently, and there is no guarantee how long CMOS RAM contents may remain intact once the battery is removed. Always be prepared to restore CMOS settings from scratch before removing the CMOS backup battery.

Lithium CMOS backup batteries are typically rugged and reliable devices whose greatest threat is simply old age. Since lithium cells are the primary type, they can not be recharged, so they MUST be replaced. Under most circumstances, there only a few symptoms that account for the majority of backup battery problems.

Checking the CMOS backup battery - It is usually a simple matter to check the CMOS backup battery. Power down the system and expose the motherboard. Locate the CMOS backup battery and find the two battery terminals leading from the battery to the motherboard. Measure the voltage between those two terminals - you should read between 2.5 to 3.7 Vdc. If the backup battery voltage is correct, there may be a software program or motherboard failure. If the backup battery reads low, replace the battery. If the battery discharges again quickly, there is a problem on the motherboard which is shorting the CMOS backup battery.

NOTE: Do not remove the CMOS backup battery from the motherboard - this will clear your CMOS configuration and make it difficult for the system to boot until the CMOS settings are restored.

Symptom 8-1. You see an error such as; "System hardware does not match CMOS configuration". For some reason(s), the BIOS has identified different hardware than that listed in the CMOS Setup, or the CMOS RAM contents have been lost. Start by checking your CMOS RAM contents through the CMOS Setup routine. Make sure that the CMOS Setup is configured properly (configuration errors can happen frequently when new drives or RAM is added to the system). Remember to save your changes to CMOS RAM before exiting the Setup routine. If the CMOS RAM contents won’t hold, check the battery connector to see that the battery is secure. A loose or corroded battery connector may effectively "disconnect" the battery - even if the battery is working perfectly. If the CMOS RAM contents still won’t hold, you should replace the CMOS backup battery outright. When replacing the battery, be sure to install the new battery in the proper orientation, and verify that it is secure in its connector.

NOTE: This error often happens when RAM is added to the system - even though there is no entry for installed RAM anywhere in the CMOS Setup. Try to "exit saving changes" though you may not have actually changed any settings.

Symptom 8-2. You notice corrosion from the CMOS battery on the battery holder and motherboard. This frequently occurs with older motherboards (i.e. i386 and i486 vintage motherboards) which have been stored for prolonged periods. The battery has ruptured and leaked onto the holder, or onto the motherboard itself. Batteries are VERY caustic to metals, and chances are that any traces or solder connections that have come in contact with the battery leakage have been ruined. Unfortunately, this also means that the motherboard has been ruined, and must be replaced.

NOTE: If you’re planning to remove and store a motherboard for any period of time, take a <PrintScreen> of all CMOS Setup pages before removing the motherboard, then store the old motherboard with the battery removed. You may place the battery in a small, heavy-gauge plastic bag at the bottom of the motherboard’s anti-static box. When resurrecting the motherboard later, you can replace the battery and restore the CMOS settings from your printed record.

Symptom 8-3. The system configuration is lost intermittently. A lithium battery generally produces a very stable output voltage until the very end of its operating life. When the battery finally dies, it tends to be a permanent event. When a system looses its setup configuration without warning, but seems to hold the configuration once it is restored, a loose or intermittent connection is suggested. Turn the PC off and unplug it. Check the battery and make sure it is inserted correctly and completely in its holder. A coin cell should fit snugly. If the cell is loose, gently tighten the holder's prongs to hold the cell more securely. Make sure to remove any corrosion or debris that may be interfering with the contacts. High-quality electrical contact cleaner on a moistened swab is particularly effective at cleaning contacts. When the battery is attached by a short cable, see that the cable is not broken or frayed, and make sure it is inserted properly into its receptacle. If problems persist, replace the CMOS backup battery.

Symptom 8-4. The backup battery is going dead frequently. This is a rare and perplexing problem that is often difficult to detect because it may only manifest itself several times a year. Ideally, a lithium coin cell should last for several years (perhaps 3 years or more). A lithium or alkaline battery pack can last 5 years or more. When a system looses its setup more than once a year due to battery failures, it is very likely that an error in the motherboard design is draining the backup batteries faster than normal. Unfortunately, the only way to really be sure is to replace the motherboard with a different or updated version. Before suggesting this option to your customer, you may wish to contact technical support for the original motherboard manufacturer and find out if similar cases have been reported - and if so, find if there is a fix or correction that will rectify the problem.

Symptom 8-5. You see a "161" error or message indicating that the system battery is dead. Depending on the particular system you are working with, there may also be a message indicating that the CMOS setup does not match the system configuration. In either case, the backup battery has probably failed, and should be replaced. Remember to turn off the system before replacing the battery. Once the backup battery is replaced, restart the system. You will likely receive a message that the CMOS setup does not match the system configuration. Restore the configuration from paper notes or a file backup. The system should now function normally.

Besides providing power to backup the system's configuration, notebook and sub-notebook computers rely on batteries for main power when operating away from AC. Such power is typically provided from a battery pack installed from the bottom or side of the computer. The requirements for battery packs are ever-more stringent - packs have to provide as much power for as long as today’s technology will allow, yet be as light and small as possible. Further, today's battery packs must be quickly rechargeable, and offer a long working life through hundreds of recharging cycles. The three battery technologies best suited to these requirements are nickel-cadmium, nickel metal-hydride, and lithium-ion.

The Nickel-Cadmium (NiCd) battery is one of the most cost-effective power sources in mass-production today. Large NiCd battery packs have been widely used in mobile computers (primarily laptops and notebooks) as a main power source. Since NiCd cells can be manufactured in almost limitless shapes and sizes, they are ideal for systems requiring unusual battery configurations. Although NiCd batteries initially cost more than primary batteries, they can be recharged often - usually recovering their initial cost many times over.

Nickel-cadmium batteries are secondary (rechargeable) devices using an anode of nickel hydroxide and a cathode consisting of a specially formulated cadmium compound (Fig. 8-3). The electrolyte is made of potassium hydroxide. NiCd cells can supply up to +1.2 Vdc each with ampere hour ratings from 500 mAh (0.50 Ah) to 2,300 mAh (2.30 Ah). Energy densities in NiCd cells can approach 50 Wh/kg (23 Wh/lb). Respectable ampere-hour ratings allow NiCd cells to supply sizable amounts of current, but their inherently low energy density means that NiCds must be recharged fairly often.

The NiCd memory effect is a unique phenomenon that is not entirely understood. In operation, a NiCd battery can develop a "memory" which serves to limit either the capacity or terminal voltage of a cell. As you might expect, either limit can result in problems with the battery. Voltage memory is generally caused by prolonged charging over a period of weeks and months. High ambient temperatures and high charging currents can accelerate this condition. In effect, the battery is charged for so long, or at such a high rate or temperature, that the efficiency of the electro-chemical reaction is impaired. As a result, the battery suffers from low terminal voltage.

The memory capacity problem is probably more widely recognized, and is usually expressed as the loss of a NiCd's ability to deliver its full power capacity. The generally accepted cause of capacity problems is the result of frequent partial battery discharge, followed by a full recharge. Over several such cycles, the battery "learns" that only a portion of its capacity is used. This renders the battery unable to deliver a full discharge when needed. Although the chemical reason for memory capacity is not fully understood, it is believed to be caused by oxidation reactions which temporarily coat the electrodes with non-reactive chemical compounds. Fortunately, the memory effect is usually temporary, and can usually be cleared by forcing the battery through several full discharge/recharge cycles. If you are in the habit of using your notebook or laptop PC until you receive low-battery warnings, you will probably not have to worry about NiCd memory problems. It is interesting to note that the newer nickel metal-hydride batteries do not seem to suffer from memory problems.

NiCd cells also have a very limited charged life when sitting idle. While alkaline and lithium cells can hold close to their original charge for years, NiCds will loose approximately 25% to 35% of their remaining charge each month. After several months of inactivity, a NiCd battery pack will need to be recharged before use. As a general rule, you should fully recharge any new or rarely used NiCd battery or battery pack prior to use. Today, NiCd batteries have largely been phased out of mobile computer use in favor of NiMH and Li-ion batteries. Table 8-1 illustrates a comparison of mobile battery features.

Nickel metal-hydride (NiMH) batteries are a somewhat newer type of rechargeable battery designed to offer substantially greater energy density than NiCd cells for mobile computer applications. Since their introduction in 1990, NiMH cells have already undergone some substantial improvements and cost reductions which have made NiMH the dominant type of battery for mobile computers.

NiMH batteries are remarkably similar in construction and operating principles to NiCds. A positive electrode of nickel-hydroxide remains the same as that used in NiCds, but the negative electrode replaces cadmium with a metal-hydroxide alloy. When combined with a uniquely formulated electrolyte, NiMH cells are rated to provide at least 40% more capacity than similarly sized NiCd cells. NiMH batteries can provide +1.2 Vdc with discharge ratings from 800 mAh (0.80 Ah) to more than 2,400 mAh (2.40 Ah) at continuous discharge currents of 9 A or more. Energy densities can exceed 80 Wh/kg (38.1 Wh/lb). This means a NiMH battery can power a laptop and support additional features (i.e. a larger active-matrix color display) for longer periods of time. NiMH batteries do not seem to suffer the "memory effects" that plague NiCd batteries, but NiMH has a shelf life of only a few days - so you’ll need to keep your NiMH batteries fully charged before traveling.

Lithium-ion (Li-ion) batteries are a relatively recent development, but they are now readily available for the newest mobile computers. The formulation of the Li-ion battery allows 20-30% more running time than a similarly-sized NiMH battery (at about 115 Wh/kg), and retains a charge for a long time while "on the shelf". Li-ion batteries are also free of the "memory effects" found in NiCd batteries, and will last through well over 1200 recharge cycles.

Zinc-air batteries are a new development in mobile battery design, and the batteries now appearing in the field offer almost twice the energy density of Li-ion batteries (at a whopping 220 Wh/kg). In actual practice, however, zinc-air batteries have proven extremely large and heavy. They are also quite expensive. These factors have kept zinc-air batteries out of most small mobile systems. Still, the high energy potential of zinc-air will keep development active. Over the next few years, Li-ion and zinc-air batteries should become the major power sources for mobile systems.

Rechargeable batteries can and do fail eventually. The process of discharge and recharge generates physical stress in the battery which will eventually wear it out. As a rule of thumb, a NiCd battery will last from about 3 to 5 years (through 500 to 1500 complete charge cycles). However, proper charging in a cool environment can extend battery life much further (up to as much as 10000 complete charge cycles have been reported). Over the life of a rechargeable cell, microscopic "whiskers" of conductive compounds develop between the electrodes. Ultimately, these deposits work to short-circuit the cell. Although "zapping" techniques have been developed using brief surges of current to remove these deposits, such techniques are very risky since the battery stands a good chance of exploding. Another failure mode is the premature loss of liquid electrolyte during high-current or high-temperature charging. Improperly designed "quick-charge" chargers can drive a battery so hard that electrolyte starts to corrode the battery's pressure relief vent. If the vent is damaged or frozen in the open position, electrolyte will continue to evaporate, and the battery will fail.

Battery life is effected by the current drawn by a computer - greater current draw results in shorter battery life, and vice versa. A large portion of battery troubleshooting is to ensure that your system setup is adequate. The following steps should help you to optimize battery life:

• Take advantage of special power modes like suspend or hibernation. These modes use very little power and should be selected when you’ll be away from the running laptop for any period of time.
• Remove or disable any unnecessary devices in the laptop. For example, you may not need that PCMCIA modem card or sound card during that flight cross-country, so remove the card. If you can disable unneeded devices (i.e. shut down power to the built-in infra-red communication unit), that will also save substantial power.
• Use the lowest screen brightness that you are comfortable with by adjusting the display's brightness and contrast control(s).
• Backlights gobble up substantial amounts of power, so set a short time-out interval for the backlight (1 or 2 minutes is often a good selection).
• Light characters and images on a dark background generally consumes less power than dark characters or images on a light background. Try setting your screen mode to a "light on dark" configuration. If you’re using Windows 95, select a dark color scheme.
• The hard disk drive is another major power user - not only by spinning, but during spinup as well. Select a moderate time-out interval for the hard drive (not so long where it spins forever, and not so short where it is constantly starting). Otherwise, you will waste more power constantly spinning up the drive than you save by turning it off. Also, constant starting and stopping can reduce the life expectancy of the drive.
• RAM consumes much less power than hard drives, so try setting up a disk cache or RAM disk to reduce the number of disk accesses. This allows the hard drive to shut down fairly quickly and not require access for a relatively long period of time.
• Microprocessor speed can be a serious drain on battery power. If your laptop computer allows you to select processor speed, use the slowest speed possible for all but the most demanding applications. Most word processors and conventional DOS utility software runs just fine with slower processor speeds.
• Most mobile batteries have trouble retaining their full charge capacity when left unused for prolonged periods of time. For example, IBM tests suggest that after a one-year shelf life at room temperature, a Li-ion battery retained 95% of its original capacity (about 90% for NiMH). If you purchase several batteries for a mobile computer, be sure to alternate the use of each battery.

When discussing batteries as main power sources, not only are the batteries or battery pack involved, but a whole host of other circuitry is included as well (such as battery charging, battery protection, and power management circuits). As a result, you should understand that problems running or charging the battery may be originating outside of the battery compartment itself. Since batteries power notebook and sub-notebook systems, trouble may be on the motherboard (where most charging and power management functions are located).

Checking the battery pack - when the battery refuses to take or hold a charge, it will often be necessary for you to verify the integrity of your mobile battery. The following steps outline the procedure:

1. Power down the laptop or notebook computer and remove the battery pack according to the instructions for your particular system.
2. Once the battery pack is removed, measure the voltage between battery terminals. If there are more than two terminals (as in Fig. 8-4 for an IBM ThinkPad battery), be sure to measure across the proper two terminals. For the example of Fig. 8-4, you would measure across pins 1 and 4. If you read 0 Vdc, the battery pack is defective and should be replaced.

NOTE: The remaining pins on the battery pack are used for thermal sensors and other communication between the mobile PC and the battery.

3. If the voltage across the battery terminals is less than the optimum value (usually less than +11.0 Vdc), the battery pack has been discharged through self-discharge (being left on the shelf) or use in the PC. Recharge the battery pack. If the voltage is still less than what the fully-charged voltage should be after recharging, replace the battery pack.
4. If the voltage is more than +11.0 V dc, measure the resistance between the thermal sensor and ground terminals (pins 3 and 4 in Fig. 8-4). The resistance should be about 4 to 30 Kohm. If the resistance is not correct, the thermal sensor has failed. This can make it impossible to charge the battery properly, so replace the battery pack.

5. If the resistance is correct, the battery charging circuit has probably failed.

Symptom 8-6. The battery pack does not charge. In this type of situation, the computer may run fine from the AC-powered supply, and the system may very well run from its on-board battery when the AC-powered supply is removed. However, the battery pack does not appear to charge when the AC supply is connected and running. Without a charge, the battery will eventually go dead. Remember that some computers will not recharge their battery packs while the system is on - the computer may have to be turned off with the AC supply connected in order for the battery pack to charge. Refer to the user manual for your particular system to review the correct charging protocol.

Your clue to the charging situation comes from the computer's battery status indicator. Most notebook/laptop systems incorporate a multicolor LED or an LCD status bar to show battery information. For example, the LED may be red when the small-computer is operating from its internal battery. A yellow color may appear when the AC-powered supply is connected to indicate the battery is charging. The LED may turn green when the battery is fully charged. If the battery status indicator fails to show a charging color when the AC-powered supply is being used, that is often a good sign of trouble. Table 8-2 lists the status indicators for an IBM ThinkPad (check the user manual for your particular computer).

Check the battery pack with all computer power off. Make sure that the battery pack is inserted properly and completely into its compartment. Also check any cabling and connectors that attach the battery pack to the charging circuit. Loose or corroded connectors, as well as faulty cable wiring, can prevent energy from the AC-powered supply from reaching the battery. Re-seat any loose connectors and re-attach any loose wiring that you may find.

After you are confident of your connections, you should trace charging voltage from the AC-powered supply to the battery terminals. If charging voltage does not reach the battery, the battery can never charge. Set your multimeter to measure DC voltage (probably in the 10 to 20 Vdc range) and measure the voltage across your battery pack. You should read some voltage below the pack's rated voltage because the battery pack is somewhat discharged. Now, connect the computer's AC-powered supply and measure voltage across your battery pack again. If charging voltage is available to the battery, your voltage reading should climb above the battery pack's rated voltage. If charging still does not seem to take place, try replacing the battery pack which may be worn out or damaged. If charging voltage is not available to your battery pack, the charging circuit is probably faulty. Replace the charging circuit. Since the charging circuit is typically located on the motherboard, it may be necessary to replace the entire motherboard assembly.

Symptom 8-7. The system does not run on battery power, but runs properly from main (AC) power. This symptom usually suggests that your computer runs fine whenever the AC-powered supply is being used, but the system will not run from battery power alone. The system may or may not initialize depending on the extent of the problem. Before you disassemble the computer or attempt any sort of repair, make sure that you have a fully-charged battery pack in the system. Remove the battery pack and measure the voltage across its terminals. You should read approximately the battery voltage marked on the pack. A measurably lower voltage may indicate that the battery is not fully charged. Try a different battery pack, or try to let the battery pack recharge. The charging process may take several hours on older systems, but newer small-computer battery systems can charge in an hour or so. If the discharged battery pack does not seem to charge, refer to Symptom 8-6.

When you have a fully-charged battery, check to be sure that it is inserted completely and connected properly. Inspect any wiring and connectors that attach the battery pack to its load circuit. Faulty wiring, corroded connections, or loose connectors can cut off the battery pack entirely. At this point, it is safe to assume that battery power is not reaching the laptop circuit(s). In this event, the battery charging/protection circuit may be defective and should be replaced. If the circuit is incorporated into the motherboard, the motherboard should be replaced.

Symptom 8-8. The system suffers from a short battery life. Today's small-computers are designed to squeeze up to 6 hours of operation (or more) from every charge. Most systems get at least 2 hours from a charge. Short battery life can present a perplexing problem - especially if you do a great deal of computing on the road. All other computer functions are assumed to be normal.

Begin your investigation by inspecting the battery pack itself. Check for any damaged batteries. Make sure the battery pack is inserted properly into the computer, and see that its connections and wiring are clean and intact. Try replacing the battery pack. Keep in mind that rechargeable batteries do not last forever - typical NiCd packs are usually good for about 800 cycles, NiMH packs are often suitable for 500 cycles, and Li-ion packs are usually rated for 1200 cycles. Fast-charge battery packs are subject to the greatest abuse and can suffer the shortest life spans. It is possible that one or more cells in the battery pack may have failed. The battery pack may also have developed a "memory" problem. Try several cycles of completely discharging and recharging the pack. If the problem remains, replace the battery pack.

The computer's configuration itself can largely determine the amount of running time that is available from each charge. The CPU, the display (and its backlight), the hard drive, floppy drive/CD-ROM drive access - each of these items consume substantial amounts of power. Many mobile computers are designed to shut down each major power consumer after some preset period of disuse. For example, an LCD screen may shut off if there is no keyboard activity after 2 minutes, or the hard drive may stop spinning after 3 minutes if there is no hard drive access, and so on. Even reducing CPU clock speed during periods of inactivity will reduce power consumption. The amount of time required before shutdown can usually be adjusted through setup routines in the computer, or through the operating system. See the "Conserving mobile battery power" section above.

Symptom 8-9. The battery pack becomes extremely hot during charging. As you learned earlier in the chapter, current must be applied to a battery from an external source in order to restore battery charge. When a battery receives significant charging current (during or after the charging process), its temperature will begin to rise. Temperature rise continues as long as current is applied. If high charging current continues unabated, battery temperature may climb high enough to actually damage the cells. Even under the best circumstances, prolonged high-temperature conditions can shorten the working life of a battery pack. Today's high-current charging circuits must be carefully controlled to ensure a full, rapid battery charge, but prevent excessive temperature rise and damage.

Battery packs or compartments are fitted with a thermistor (a temperature-sensitive resistor). When the battery pack is fully charged, the thermistor responds to the subsequent temperature increase and signals charging circuitry to reduce or stop its charging current. In this way, temperature is used to detect when full charge had been reached. It is normal for most battery packs to become a bit warm during the charging process - especially packs that use fast-charge currents. However, the cell(s) should not give off an obnoxious odor or become too hot to touch. Hot batteries are likely to be damaged. In many cases, the thermistor (or thermistor's signal conditioning circuitry) has failed and is no longer shutting down charge current. Try another battery pack. If the new pack also becomes very hot, the fault is in the charging circuit which should be replaced. If the new pack remains cooler, the fault is probably in the original battery pack.

Symptom 8-10. The computer quits without producing a low-battery warning. Computers are rarely subtle in regard to low-power warnings. Once a battery pack falls below a certain voltage threshold, the computer initiates a series of unmistakable audible (and sometimes visual) queues that tell you there are only minutes of power remaining. Such a warning affords you a last minute opportunity to save your work and switch over to AC power if possible. If you choose to ignore a low-power warning, the system will soon reach a minimum working level and crash on its own - whether you like it or not.

Mobile computers measure their battery voltage levels constantly. A custom IC on the motherboard is typically given the task of watching over battery voltage. When voltage falls below a fixed preset level, the detector IC produces a logic alarm signal. The alarm, in turn, drives an interrupt to the CPU, or passes the signal to a power management IC which then deals with the CPU or system controller. Once the alarm condition reaches the CPU, the computer typically initiates a series of tones, flashes a "power" LED, or sometimes both (see Table 8-2).

Most PCs produce at least one beep during initialization in order to test the internal speaker. If you do not hear this beep, the speaker or its driving circuit may be damaged. Try replacing the speaker, then try replacing the motherboard. When an audible beep is heard during initialization, there is probably a fault in the computer's battery detection or power management circuits. Try cleaning the battery contacts first, then try replacing the motherboard.

Most types of batteries use metals and electrolyte chemicals which are harmful to the environment. As a consequence, many states and provinces have enacted legislation which prohibits the dumping or discarding of batteries (especially lead-acid, NiCd and alkaline). NiMH and lithium batteries are somewhat less toxic, but can also often be recycled. In order to help support a cleaner environment, many vendors who sell PC batteries are accepting returns of the old defective batteries which are recycled. For example, IBM supports the Reusable Battery Recycling Center (at 770-984-0708). 1-800-Batteries (another major battery vendor) accepts returns (at 408-879-1930).

That concludes Chapter 8. Be sure to review the glossary and chapter questions on the accompanying CD. If you have access to the Internet, point your web browser to some of the contacts below:

Direct Power: http://www.dpp.com/index.html

1-800-BATTERIES: http://www.800batteries.com/index2.html

Duracell: http://www.duracell.com/

Energizer: http://www.energizer.com/

Tadiran: http://www.tadiranbat.com/

Rayovac: http://www.rayovac.com/