I have a John Deere Z255 zero turn mower that is three years old and I am having an issue with the battery not getting charged. The battery is new (May 2017) and charges ok when jumped with cables. I have tested the charging wires from the stator and get almost 4 amps on the DC side and 15 volts on the AC side; however, when I test the battery voltage, I get a little over 12 volts with the engine off and the same reading with the engine running at about 3600 RPM instead of the 13-14 volts I should be getting.