HELP!!! Galaxy S3 i747M battery problem on android 4.4.2

when i charge my phone through the night and disconnect it in the morning it instantly drops from 100% to 2% and again it instantly rises to 100% and the battery last me like one hour with the screen off and then it powers off. so when it powers off i turn it back on and its like at 65% and when it powers off again i turn it on and its like at 30% ...
so whats wrong with my phone cause i know its not the batery because i bought i new one.
i hope someone can help me.

Bell/Virgin i747m to nj1 question

Hey, I'd like to use CM12.1 official nightlies but I have a bell(well, virgin) phone with the ne6 bootloader and I'd like to be able to upgrade to nj1 but I've searched and no one has written anything about it, only the American version. Can anyone please explain clearly how I go from NE6 to NJ1 to get my phone or equivalent to run CM12.1? :(