Hello Bob,
Might be software or hardware. First backup your device to a computer with iTunes. Then preform a DFU restore. Run it for a bit and see if its working as it should. Second, are you using and have you been using certified cables? Non MFI certified cables do not have an IC chip that cleans and regulates the voltage coming into your device. This can lead to the symptoms you are describing. Get a USB amp meter or take it to a local shop. If it draws the proper current then I think you have a damaged board on your battery that acts as your "Gas Gauge"
Good luck
Holger