Today I turned the key and let the instruments initialize and after initialization was complete the fuel gauge indicated full which is correct. I then started the engine and the fuel gauge immediately indicated empty. I then turned the engine off and went through the procedure again and the fuel gauge indicates full but when started the engine the gauge again indicated empty. I did this several more times and the gauge always indicates full after it is initialized but is sporadic after starting the engine, sometimes showing empty and other time showing full. The battery is maintained on a battery tender. In addition, I replaced the original battery with a Sears Diehard in 2013 and it is properly grounded. I have searched fuel gauge failures but have not come across this particular problem. Any and all help is appreciated.