I had all of the problems listed in this forum. Phone said the SD card was unmounted, battery draining after only a few hours, and getting hot. I removed the battery and put it back in but this did not help. Finally, took it to a T Mobile store where they did a factory reset. After that, we discovered my SD card was not working but didn't know why as I never had a problem with it before. Replaced the SD card and then recalibrated the battery as directed by juo78. Phone is now fixed and battery has not needed to be charged for 2 days now. This was better than before it broke where I could get 1 1/2 days at the most. Right now it is still 1/2 charged.
Let's hope I don't have this problem again as I don't know what fixed it. Hoping it was the battery recalibration rather than the factory reset cuz that was a pain.