I'd like to say that there IS variaties on battery life performance from ROM to ROM, because I am same sensative as bstylz911 on battery life and I did notice that it does matter on which ROM is using.
Generally speaking, a LITE ROM will be more battery friendly than a FULL ROM, if you don't install and run unnessacery programs on it. On the other side, a well cooked WM6.5 ROM on same load, due to its enhanced core, will be better than a WM6.1 ROM for power management.
I can not say which is the best because I did not flash many ROMs in recent two months, but based on my past experience SAKAJATI's Apr. 20th WM6.1 Rhodium Lite ROM has been best for me, another one maybe from -888-, the first replyer for your post, telling from that it is a really lite ROM, maybe there are others recently released, please just read and search 'battery' on each ROM thread for user's comments.
Beside ROM itself, there are many other factors that could affect battery life, please check this thread and all links from the thread for more information:
[res] Battery Conservation Fanatic thread.
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