UPDATE (7/9/09): I've tried everything, a hard reset of my phone, letting the phone fully discharge then recharge, and it improved a little bit, but not much. I called T-Mobile and they admitted it's a known issue. I expect the next software update to take care of this.
I'm a T-Mobile customer and own the G1 phone. Recently, an over-the-air update was released for the Android operating system, version 1.5 or "Cupcake". Everything's been running smoothly for me thus far besides a couple complaints, but the main thing I found was my battery would only charge up to about 64% and then charge VERY slowly. I'm talking it went from a couple hours to perform a full charge to around 8-10 hours!
After a few days of this happening I thought I would just restart the phone (since that seems to be the answer to almost any techy device) and the battery said it was fully charged, 100%, which led me to believe it was a software issue. The battery was fully charged, but the software didn't know it. So I did some digging and it seems a lot of people had this same problem.
Turns out downloading the updated operating system on a less than fully charged battery led the new OS to believe the battery is fully charged at whatever percentage you had when you updated your phone. Sounds like someone at Google would have thought of this and prevented this from happening, but I guess they were eager to push this out so they missed it. Anyway, one solution someone suggested is to just let your battery fully drain to the point your phone shuts off from lack of battery, then just fully recharge it. I'm told this will solve the problem and allow the OS to re-calibrate itself, I guess it makes sense logically. So far I've drained mine and it's charging right now, I'll report back on how it goes.
