You rarely need to worry about the computer battery, I've only seen it go dead in a long unused computer, in fact as long as it's plugged in to a power source the computer draws power from the wall not using that battery, at leats most do. (Which is a reason to unplug it if you ever open it). All the battery is for is to save your CMOS settings, which are ocmputer specific settings, and the time. So even without the battery your computer will run, but things liek the time and date will be wrong. If you ever do have to worry about it, take it in to get it changed. I'm not even sure how necessary it is in newer computers, well I won't go into why but the needs for a CMOS are virtually non existent in todays technology. Being three years old, it may be more than a legacy, I'm not sure. But for the most part the battery is almost never even used, except to reset BIOS settings (which CMOS used to store before they had technology for other things).
