The key to solve everyones battery problems... 3 easy steps!!!
I did this and i get 2 days HEAVY use, and I MEAN HEAVY:
DISPLAY 3H 56 MINUTES
CALLS    56 M
STAND BY  2 DAYS 2 HOURS
1.) Throw away the OEM charger. its a bin part for their bluetooth head sets.
2.  go get an HTC usb USB wall charger, or one that produces a FULL 1 AMP (1000 ma) on the output, with 5v. any UL device will say the output on the charger itself.
WHY? the captivate is rated at 1000 ma, or 1 amp. the battery is 3.7 volt @ 1500 MA !!!! and here is the problem... SAMSUNG GIVES YOU A 700 MA CHARGER!!! WTF SAMSUNG?
3.) retrain your battery. the longest part of the process!!!
wait for your battery to go completely dead!!! until the device shuts off!!!
charge it with the new wall charger for 12 hours... with it off... I mean off...then:
---use your phone normally, u wont notice a change just yet. use it over a day as u normally would. run the battery completely dead again.
do this for 2 weeks strait. im serious. it sucks, but u have to do this.
after about the 6th day, you will notice that your battery will go a little more each day.
after the 2 weeks, you should have about 25% more life. why?
OEM gives you a 700 ma charger @ 3.7 volts. your battery is rated at 1500 ma.
Rule of thumb for charging? 2/3 the capacity of the battery for ma, with oem your getting less than half.
THIS IS WHY YOUR BATTERY SUCKS!!!! ITS THE CHARGER!!!
ALSO, there is an error in the charging display when the phone is on. when you get that message on the screen "battery is full, unplug charger" turn off your phone while still being plugged in. the battery picture will show the battery still charging, and it has about 15 percent more to go... dont believe me? try it yourself... ONLY WHEN THE PHONE IS OFF WILL IT CHARGE IT 100%, and the battery icon will say 100% when fully charged.
then u can try these things to:
First things first, get an app killer. 
dont run those INSTANT UPDATE facebook/twitter acounts, they should only update when the screen is on (a setting in the app killer). 
live wall paper--if you must, run one thats dark in color. i personally use the starfeild, as it is mostly black and it is a small file.
i have a brightness toggle, goes from full to minimum with a touch. i dont use the automatic screen adjustment, for some reason it dims it in sunlight and brightens in the dark... it should be reversed if u ask me. 
So thats it. i have done this with my battery, it was built in august (the battery) and the preformance is outstanding.