IPhone 4S Battery keeps dying 20-25%?

My dads had the 4s since its come out and passed it down to me a few months before the 5 came out, the battery has always been fine for him and me since last week, my phone turns of at 20-25% like the battery has died and as soon as I plug it in it turns back on straight away and starts charging?

My old iPod was like this, you can go to the apple store and ask them to replace your battery for a new one. This may or may not cost. This probably happened because you are over charging it never leave your phone on charge when you go to bed.

  • I have an iphone 4, battery keeps dying? How do i stop my battery from dying even though i aint even using it. I keep my cel in my pocket while i'm working, but when i go take my break its already at 50% but it was 100% when i started working just 2 hours before
  • My iPhone keeps dying at 30-40%? It this a battery malfunctioning? I sent in a diagnostic test to Apple online and they said my battery passed the test and it's working fine. Any fix? I already reset this with the power and home button but no use! Should I trade in for a new one?
  • My iphone battery keeps dying and I'm not using it? It is connected to the Wi-Fi in my house, so not 3G. It will be 100% before I go to bed, then by the time I wake up in the morning the battery has died. The battery is draining when I'm not using it? Today I charged it to 95%, was home for a couple of hours, didn't use it and now it is at 4%?! What is wrong with it? I don't have any new apps or anything, it's never done this before!
  • Iphone keeps dying when I take it off charge? Charges normally and as soon as I take it off charge it switches off instantly. Any fixes or do I have to take it to the Apple store?