My battery appears to last forever. On a couple of occasions though it's gone flat over the night (actually I noticed the 'low-battery' warning sound before it died on me). The last time it happened I plugged in the charger and checked with 'top' in an xterm. 'vi' was running with 100% CPU, and then I remembered that I had used 'vi' the day before and quit by terminating the xterm.. not a good idea.
In other words, if it seems to go unusually fast through the battery, check if there's some application looping. And if so, try to find out what caused it.