Battery life on D2 GB was better than liberty 1.5, however there was a known issue on 1.5 that caused some instability and massive battery draining. In comparison to the stock froyo builds with blur, the GB build is a massive improvement, however I'm still not seeing the same battery life I was seeing on Fission or UDRC2, no matter what tweaks I've performed on GB. Now running Liberty 2.0 after I goofed up my GB installation (playing with a theme broke some framework stuffage, restoring a recovery broke everything, no idea why) and my battery life is about double what I got on GB.
The blur framework and system files put a much heavier load on the system than what a stock system does, hence the reduced battery life. Tweaks to voltage, governor, and clock settings help, however it's not enough yet. Also, since all hardware is slightly different (due to production tolerances), please keep in mind that YMMV.