[Q] Charging only to 85% topic

I have searched through many of the forums and have found this problem all over with no clear solution. So I thought to start a fresh one. I have a Samsung Galaxy S3 that was given to me. The battery life was only a few hours so he got a new phone. Anyhow I have purchase 2 different batteries and both only charge to 85%. The first one would only charge to 100% once and when I unplugged the phone it dropped to 85%. The second battery charged to 98% the first charge. I let the battery completely drain and recharged with the phone off. Went to 100% no problem. Turned the phone on and it said 85% charged. With both batteries sometimes I can unplugged the phone and after a little while of waiting it goes up to 95%. Tried multiple charges to see if it had something to do with that as well. I have attempted to clear the cache files from recovery mode multiple times. I cannot root the phone to delete the battery bin file. I have attempted many times and this one just won't do it. Android version: 4.4.2 Baseband version: I747UCUFNJ1, I cannot get this damn thing to root to save my life. I'm just frustrated. I was hoping to get a nice phone for free but with it only charging to 85% i just can't accept that. Does anyone know what I can do about this?:confused: