I had this problem with my E815 awhile back. I had bought an extended battery. Worked really well for awhile but eventually burnt out and wouldnt charge. It would keep reseting and such. THEN when I eventually began to use the stock battery it would restart as well but it would still charge. I discovered this to be because the battery was moving just a little out of place so it wouldnt stay connected properly. To fix this I took a little piece of rubber and placed it inbetween the battery and the battery door. Since then I've purchased an official extended battery that works fantastic.
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