Small Engines (Lawn Mowers, etc.): John Deere 345 Charging/Battery problem, john deere 345, printed circuit board

Question
I have the Kawasaki 20HP liquid cooled twin engine in this, and for a couple years now, the battery is always losing the charge.  I thought it was due to not removing the battery and storing it over the winters (I'm in Ohio), and a cell going bad, but I just put ANOTHER new battery in this year, and it lasted about 2-3 weeks before it too lost its charge.  The dealer replaced the printed circuit board or something, which they said was the problem, last year, but this year, same thing is happening.  I checked the terminals at the battery while running, and it was about 13.2 Volts, which made me think the alternator was okay.  Any help ?

Answer
I have to admit charging systems are not my strong suit. But in most 12v systems 13.2 is borderline. When are you experiencing the weak battery, after it has sat between mowings, or during a shut down, and restart during operation? Heres a few things to check, if it is during an inactive time, you have a current draw pulling down the battery as it's sitting. You can disconnect a battery cable with everything off, and place a volt meter between the cable, and battery see if your showing a current draw with everything shut down. From there you'll have to do some back tracking to see what is pulling the power, and drawing down the battery. If it is during operation then you do have a charging system malfunction, and must isolate the failing component. One more thing, are you being fooled by either a poor connection, or a starter thats over drawing?  Either of those two situations will be rectified by a new battery sometimes, just because it is at it's peak of power when new. As a battery gets older it begins to loss cranking amps. I have also seen more than one mechanic go crazy chasing a starting system problem when the problem was actually a compression release not operating correctly, and releasing head compression during starting. But each time due to the new battery it would have enough power for a little while to over come the compression. Just somethings to check.......Tom