Could be the stator,,take a reading off the battery using a DVM with the engine off,,then take a reading with the engine running at half throttle or so,,the voltage should be about 12v with it off and closer the 14 or 15v with it running,,if the voltage does not go up at least a few volts running then I would say you need to look at the stator and the wiring thereof....I believe its under the flywheel but not 100% sure.
You can do an OHM test on the stator coil(wires) using the DVM to verify if its bad or not,,Im not sure what the value would be on that motor,,you would have to google it up.
You could also have an slow drain when the mower is off,,way to check that is using a DVM in amp or mA mode,remove the positive from the battery and insert the DVM in series between positive lead and positive battery lug,,you should not see any mA or amperage indicating a high resistance or short somewhere in the wiring.
Tom
