...I've been using BatteryPlus for a long time, on the Torch, the 9780 and now on the 9900, and it does seem to help, it offers a 'battery boost' function and other tweaks, logs etc. Using the original OS on my 9900 for the last couple of weeks, I've not had any issues w/ battery life other than the fact that of course we'd all like a longer-lasting one!! BatteryPlus is available here at CB's app store and I also must say that their customer support, when I was switching from the 9780 and having a bit of a problem upgrading, was fantastic.
The other great one to keep an eye on battery performance, temperature, memory etc is MeterBerry - also recommended.