Most batteries last 2 hours or so, unless otherwise noted. If you get an extended battery, you will get 4 or 6 or more hours, depending. But for the most part, the average laptop battery will last you about 2 hours.
i had CRAP luck with my thinkpad, i was mad cuz there was no windows key but o well, then my hard drive died(theres where ur reliability problems come in) and it didnt perform the greatest.
I've heard good and bad about IBM and Toshiba. My dad's IBM from work started smoking one night, and never worked right again. But my buddy's 10-year-old IBM laptop works just as well as the day he bought it.
And Toshiba: I used to know of a company that had 10 defective Toshiba laptops, that had serious cooling problems. But most people I know have had no problems with them.
I Have had good luck personally with both Toshiba and Dell. One DOA hard drive, but that happens all the time anyway. It was replaced in jig time. Go with a mobile CPU if your going for battery life. Stick with the P4 for preformance. You'll just need to reley on your charger more.