Why won't my ipad charge

i work at a local repair shop and we have an ipad that will not charge. we replaced the battery and the dock connector and it does not charge. if i put a charged battery in the ipad works, but when the battery dies it won't turn on. because you can't keep it charged.we do not have any genuine apple usb cords or wall warts, but we have tried all the ones we have at the shop. when we took the front glass off it broke and had to be replaced. we have tried like 2 different dock connectors and 2 different batteries. it is a white ipad 2 gsm. if the ipad is running and it is connected to a computer itunes sees it and it will sync properly. we have restored it to factory settings but it does not have ios 7 yet.