I have had terrible misfortune in the realm of battery stats. Ever since CM7 (and maybe even before) my phone is unable to figure out how much battery is left. Here is a common scenario:
Charge phone overnight, use phone throughout day, battery dies after 6-7 hours of moderate-heavy usage. I plug it in, reboot, and then it reports ~60% battery left.
Another common scenario is that it will dwindle around 5% battery or less and go up and down until it finally dies.
I know that this is a misreading of the battery and not battery drain or a rogue app because when I flash a new ROM the battery life is amazing for 1 day. The day after I flashed Team Hacksung's ICS rom, I got almost 17 hours of battery life with 2.75 hours of the display being on and 30 minutes of Google Music. I was blown away! But even then it was dwindling around 5% not knowing when it would actually run out. The day after, it was back to its old tricks of misreporting the battery percentage.
Today I charged it to 100%, unplugged it, and shut it off. Then I plugged it in while it was off and let it charge to 100% again and wiped battery stats in Clockwork mod. I'm getting ok-ish battery with that, but it's not even close to how good it was when I first flashed ICS.
Anyone have any ideas what I could try?