I am not a motorcycle mechanic, and any of the tips or techniques I list here are for the do it yourselfer. If you don't feel comfortable doing any of your own work than take your bike to a professional mechanic. Also each situation may be different so all the information may not be here.
Before begining any repair projects there are somethings you should have prepared. Always have a fire extinguisher available, floor dry to clean-up spills to prevent slipping, rags, if removing or replacing a battery something to neutrilize the battery acid, a good source of light, and ventilation. These are just a few things I might have missed something but, this is a good start. When ever you work on the bike it is a good idea to keep the bike in gear this prevents the bike from rolling forward an added measure would be to squeeze the brake lever, this will really hold the bike firm.
The first tip I have is on drilling of your exhaust pipes on the Intruder 800. The first thing I will say is where you do the drilling, all the drilling will take place at the end of the pipes the area that is black in color. You will drill three hole equally spaced in the end baffle. You could probably use any drill bit up to 3/8 or 10mm in diameter. Before ytou start any work on your bike make sure the bike is in gear this helps prevent the bike from rolling foward. Another bit of advice would be to squeeze the brake lever to engage the front brake this is just a little extra. The bit I used in my pipes was a 5/16 bit, this bit is also a tap drill for a 3/8-16 tap. I did this so if I was not satisfied with the sound I could tap the holes and install a bolts in the holes and return the exhaust back to stock. Remember when you are done with all you drilling you need to get some high temp paint and paint the hole to prevent rusting.
First off your battery is located at the bottom of your bike, just in front of the swing arm. To gain access to your battery you should put your rear tire on a 2x4 for a little extra clearance. Then start by removing the negative battery cable first doing this prevents a short, then remove the positive cable. Remove the two screws securing the bottom cover be careful at this step because the battery can slide right out. Installation is in reverse order.