I don't use MIUI anymore because of battery life but to mitigate some of the battery drain I used to under-clock the processor to 800MHz and keep the screen off (instead of letting it time out) and when possible charge it in short bursts with the screen off.
I gave up on MIUI....its a nicely themed rom with great functionality, but the down side is bad battery life. Once I switched to Oxygen Rom my battery life nearly doubled. If MIUI evers gets tweaked to extend its time off the charger I'll gladly jump back on the boat.
hmm that's so weird of you to say. I started with deck, moved to oxygen and now to miui and I'm getting better battery life with this than i ever did with oxygen or deck. Yesterday I did some testing and ended a solid 24 hours with 36% battery left on miui with matrix 5.5 kernel. I'm going to switch and try trinitys to see if I can get any better.