Friedbeef's Tech has published 15 ways to extend the battery life of your laptop.
Some are pretty obvious but others are quite interesting:
6. Run off a hard drive rather than CD/DVD - As power consuming as hard drives are, CD and DVD drives are worse. Even having one in the drive can be power consuming. They spin, taking power, even when they?re not actively being used. Wherever possible, try to run on virtual drives using programs like Alcohol 120% rather than optical ones.
7. Keep the battery contacts clean: Clean your battery’s metal contacts every couple of months with a cloth moistened with rubbing alcohol. This keeps the transfer of power from your battery more efficient.