do a little test.... before bed charge your phone until green led appears, reboot/power off and then on while still hooked up to charge. In the morning compare your up time to your awake time, make sure their not the same.

I would guess its customization and Apps that may be draining the battery. I upgraded my phone to the 1800 slim battery because i didn't want the phone to increase in size with a thicker extended battery.

You can also check your Apps in the MANAGE APPLICATIONS SETTING on your phone.

 

Where did you buy the 1800 battery?

 

HTC DROID Incredible PB31200 Accessories

 

How did you know that one would work with the Captivate? Are there certain things to look for? I'm new to having a phone where I actually have battery options (damn iPhones )

EDIT: I just looked at the one you were talking about from the site you linked... from the pictures it doesn't even look the same shape as the Samsung battery in my Captivate. Also the contacts are different.