Battery going from full to half full

[charleslongsr]

Ok guys, I was having an issue with my battery or atleast I thought it was my battery. I would charge my phone and it would be full. After some usage, nothing major and maybe 30 minutes it would be sitting on half. It hasnt been like this and I have had the phone for almost a year. Well, I have replaced the battery with an extended life battery and it is doing the exact same thing. So now I am thinking that the issue may be in the rom. Just so that im clear, it will appear to be full 90-100 then all of a sudden drop to half full. Any suggestions or should I just call sprint up?