I just bought a used 1992 Yamaha Serow dual purpose bike. When I bought it, it started just fine and rode great. Got it home, and the battery appeared to be drained. Instead of buying a charger, I decided to go ahead and just get a new battery. I bought the exact battery that comes with the original bike. I believe it was a Power Source battery. Installed it, it started the first time, and hasn´t started since. Friends have told me that I need a new alternator, b/c they assume the current one is draining the battery. Any information anyone could give would be greatly appreciated. This is my first bike, so I know pretty much nothing.