For the past year or more, I have kept my iPhone 4s on all night because I use it as my main alarm in the morning. It rarely drains more than 20 or 30%, sometimes less. Two nights ago, I charged it to 100%, but my alarm failed to go off in the morning. When I checked why, I saw that the battery had drained down to zero over 7 hours. I have charged it back to 100% but it keeps draining very quickly. This morning, it went from 100% to 63% in just two hours with no use whatsoever. I keep WiFi on, but that has been the case for the past year. Something has changed and is very wrong. Can anyone help me? Thank you.