Some users, when flashing new ROMs, have noticed that their battery life goes down a little bit. With just a simple wipe of the battery stats file, though, you can get your battery back up and running to its full capacity.
The battery stats file basically tells your phone how much battery it has left. The problem is, sometimes this file can get a little out of whack and tell your phone it's fully charged when it isn't done charging yet — so your phone will charge to, say, only 93 per cent instead of 100 per cent before stopping. If you're rooted and running ClockworkMod recovery (which most root users are), you can wipe the battery stats, giving you a fresh slate and allowing your battery to more accurately judge its fullest potential. To wipe the stats file:
- Fully charge your device, until your LED turns green or until your home screen says "Charged".
- Reboot into recovery mode. This is different on every device (I know on my Droid, I have to hold the "x" key when powering up). Google how to do it for your device, or, if you're running a custom ROM like CyanogenMod, you can reboot into recovery mode from the phone's regular shutdown screen.
- When you reboot into ClockworkMod, head to Advanced > Wipe Battery Stats and hit Yes. When it's done, go back to ClockworkMod's main menu and reboot your phone.
I've tested this myself and, while it's hard to judge what it's done to my battery life (I already get pretty rocking battery life on my Droid), I haven't seen any adverse effects, so it's worth a shot if your battery life is killing you.
Hot to Fix Battery Drain Issue on a Rooted Android Device [AddictiveTips]