You can buy a brand new battery on ebay for around $7 on ebay. If you where going to look into that theres a bit of info for you. You could also get a 3900Ma extended battery on ebay for anywhere from $10-20. The ones that are around $20 are the ones that include 2 batterys, the back, and a wall charger for the battery, the wall charger also has a usb port on the top of it.
Steve Rogers: Big man in a suit of armour. Take that off, what are you?
Tony Stark: Genius, billionaire, playboy, philanthropist.