I have a Kohler 20hp twin cylinder horizontal shaft motor in a 48" Walker mower. The engine would not turn over so I charged the batery and then load tested it. The battery failed the load test so I replaced it. The engine started right up but the voltmeter on the instrument panel is only reading slightly higher than 12 volts. I placed a voltmeter on the battery with the engine running and it is reading 12.6 volts. Is this acceptable? If not, what wires do I have to check to determine if the regulator is functioning properly.