Battery stops charging at 80 Android

Hi all, I've had my Thunderbolt for 5 months now, and everything worked fine for about the first 3. But over the past few weeks, I've noticed that the phone won't charge fully, while on or off. Using stock battery, stock original firmware. Used to be able to get to 100% overnight fine with stock HTC charger and a bestbuy Rocketfish charger. But now, I haven't seen the green "fully charged" light for over a month. The LED stays orange even after 12+ hours of charging. I even finally got the OTA update last week thinking that it may help, but it didn't change anything. I've tried battery pulls, different chargers including my old blackberry charger, LG charger, car charger from verizon, and nothing will give the battery a full charge. Phone Info app now says the phone is around 80-85% charged after a full 10 hour night.

I just recently downloaded the Battery Monitor Widget off the market and noticed that the stock HTC charger/usb cord charges at least 500+ mA initially, but when my battery gets up to somewhere between 75-78% charged, the charger only puts out below 35 mA, usually 10-20 mA. So I'm thinking that there's something wrong with the battery/sensor. Anybody else have this problem or heard about it?