No electric charge on yamaha yt 3600

[Piacentini]

Good morning,
On my yamaha yt 3600, I have to put the battery on charge all the time. Once charged, the battery is 12,5 volts. When the engine is running, Voltage is about 12,8 volts. When I am thru mowing, voltage is about 8 or 9 volts. I suppose that the alternator dont work, but I can't even find where it is. I am a backyard mechanic. Thanks for helping.

http://www.tractorforum.com/f154/yamaha-yt3600-electrical-problem-17923/

[Piacentini]

There were two problems : battery and contact. Voltage being low and increasing when the engine was set on, I thought the alternator control unit was allright. I cleaned all contacts with contact cleaner. Seems to have worked well : voltage has gone up. But battery was flawed.  I bought 4 batteries since I have that yam : only one out of 4 worked well and lasted 9 years (YUASA). Hope that helps. Thanks.