[diablo09]

Mine used to give me like a day's battery with average use. Ok, here's what i did.

I have rooted my phone, and have:
1. task manager,
2. battery monitor in status to show battery percentage,
3. start up auditor,
4. cpu info widget (with temp and speed and cpu usage),
5. app protector, and
6. 3G data usage monitor
These are always on, except for the cpu info widget that's turned occasionally on and off.
Apart from this,
1. static wallpaper (not black screen)
2. use wifi all time at home, and bluetooth when outside.
3. have brightness set to 0 when not in sun, and to about 50% when outside.
4. screen auto-rotation turned off, since i hardly use this

i installed "SetCPU" app, and here are my settings of the app:
1. when display is turned off, auto set the phone to 400 MHz speed with "conservative" mode on.
2. all other times, set the speed to 400 MHz with "on demand" mode.

i don't notice any noticeable lag for my day to day tasks, and my battery life has more than doubled.

EDIT: This is my second Captivate. I exchanged my first Captivate after about 10 days for its horrible battery life.