Strange Battery Issue?

[Chantalle Heart]

This started happening when I spent a week in BC right after I updated the software.
My phone would be at a hundred percent when I would go to sleep. When I would wake up, my phone would not be on. It would shut down sometime during the night because it had one or two percent battery left. It did that for a few days until I decided to just leave it plugged in. I use my phone alarm, so I can't just have it shut down on me when I need it to wake me up at 6am for work. So this was happening in July. Then all of a sudden it was fine. But now today I wake up and it's the same thing. I went to bed with ninety-nine percent, I wake up and my phone won't turn on. Once I powered it back up it said two percent. So for it to do this then it suddenly be fine and now start to do this again, it doesn't make sense to me.
Help?

 

[B. Diddy]

Welcome to Android Central! First, try booting into Recovery and wiping the cache partition, which won't erase any personal data. Sometimes funky things can happen after a system update, and wiping the cache partition can help resolve them. http://forums.androidcentral.com/sa...ing-into-recovery-mode-galaxy-s2-s3-tab2.html

Another thing to try would be to unmount the SD card (in Settings>Storage), remove it, and reboot, then see if the problem recurs. A corrupt card can cause things like unpredictable battery drain.

Finally, a new battery might be in order, although the fact that this behavior started right after the system update makes a battery problem less likely.