For the most part, a lot of these roms are based off of the base version and then tweaked for optimal performance. While there are some that are feature laden (ie. loaded to the kills with tweaks and background processes) and some that are fairly basic (a few features, stripped down ROMs), battery usage all depends on how you setup your phone.
I've got the Pegasus series ROM on my touch diamond and it works fine (battery life still to be tested) and I haven't noticed a serious detriment to my battery life yet as there are tweaks in place to maximize power savings.
Even with the stock ROM (Bell in my case) battery life maximization has always been an issue.
Here are a few tips to maximize battery life (applies to pretty any rom, stock or not):
1. If you don't need that fancy 3D interface, kill it and go with the basic home screen.
2. Make sure to turn off your data connection when not in use (will go into an on-demand mode if you have anything that runs in the background to get updates once in a while). Make sure WiFi is shut off as well (serious battery drain) and the same goes for bluetooth when not in use.
3. Dim your screen to the point so that's still usable (brighter screen = more power usage).
4. Put your phone to sleep when it's in your pocket instead of waiting for the default time out (press and release the power button to sleep it, do the same to wake). It might only be a 30 second difference, but it adds up a bit.
5. Reduce the number of background running applications to essential ones (ie. e-mail is essential, MSN not so much). Kill any widgets that don't really need to be active (twitter and facebook ones are notorious for sucking up battery life).
That's all I can really offer for now, the more seasoned members can help you out on what ROM is more battery friendly. I've been lurking for a bit, it's time that I start contributing.
- Michael Artelle
Tech Junkie, Tech Support Analyst, Network Administrator
Current Device(s): Motorola Xoom Wifi 32gb, Samsung Galaxy Note 2 T889V.
Retired Devices (Recent): Huawei E1691 USB 3G Modem (Wind), Samsung Galaxy Nexus S (Wind), RIM BlackBerry Curve 9360 (Wind)
Service Provider: Wind Mobile