Iphone 4s won't charge!

PLEASE READ

okay. A while ago, my iPhone 4S battery has been really bad and dying at like 50% I don't know if it has something to do with IOS 7 but my friend who has IOS 7 on her iPhone 4 doesn't have this problem.

Anyways, this means that i have to take chargers out with me constantly and charge it in public. Recently, my iPhone charger just stopped working so I used one of my mothers and it was working fine for a while and then that stopped working also.

My mom asked me to charge her iPod which doesn't have IOS7 on it. The iPod was completely dead; I plugged it in and it charged to 20% but when it turned on it stopped charging. This happens with my phone as well. It would be completely dead so I plug it in and it would charge, turn on and then just stop charging.

I am thinking that my battery effected these chargers but I am not sure. They were working perfectly fine and then suddenly just stopped. Can anyone help me please?