Galaxy S3 Mini..battery drain problem :(

Welcome to the forums!
I was thinking of buying a new battery, what do you all think?
Sounds like a great starting point to me - the symptoms certainly sound like your battery has failed.

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I know ! I can only use my phone when it is plugged in the charger. If I use it without the charger for like 5 minutes, it just turns off and is at 2 % and then keeps restarting until I plug it in the charger or take out the battery and put it back in. Plus, my charger doesn't charge it anymore, only if I kinda push it back a bit.