The ROM has the main effect on battery life other than how heavy youre using your phone. It has the effect on the battery because it is the very brains of your phone and the chefs disable and tweak certain things for better battery life. Dont ask for Chulo12's ROM that hes using, his is for the Touch Pro and would brick your phone.
However NFSFAN's ROM has very excellent battery life if you turn off the Touchresponse program (the program that makes your phone vibrate everytime you touch it). I would suggest flashing to his. You can find it here
http://forum.xda-developers.com/show...postcount=2378 this is his WM6.5 ROM
http://forum.xda-developers.com/showthread.php?t=432487 this is his 6.1 ROM.
Hope all this helps you!