I recently downgraded to a cheaper phone and now trying to sell my 4s Sprint phone. I reset it and put it up for auction. Suddenly the phone won't start up in the morning. If I press both buttons it starts up fine and starts up throughout the day, but the next morning same thing happens. It is fully charged. This never happened before. I rarely used the phone and only charged it a few times a week (which is why I decided to downgrade). I'm just concerned there's a battery problem or something. I don't want to sell a crap phone and risk getting a negative rating. It's only 9 months old. Is it still under warranty if I already switched to a different phone? I'll take it to a Sprint store tomorrow, but I thought I'd ask here first.