IPhone 4 won't charge

My iPhone 4 has all of a sudden stopped charging. It hasn't had any water damage or anything and I have tried more than one charger. The phone charges when its turned off and when it turns on it still charges until it hits 8% and then it stops. I have had it for a about 3 months and I don't have any warrenty or insurance, please help!

Ok try another home adapter or laptop usb drive or somethingv