The owners manual states in the event you discharge your battery completely, to consult with a Yamaha Service Department. I take this means that you should be careful not to over charge your battery. Am I right? To be on the safe side, I charged it at 2 amps for about 6 hours and let the long weekend of riding charge it the rest of the way.

 

If your battery ever fully discharges at any time it will be because there is a problem with the charging system, or electrical system or there is some type of discharge draining your battery. Old age will also kill a battery.

 

I accidentally left the ignition on over night.

 

Two amps at 12 volts is hard on such a small battery. I would recommend 200 to 300 mA @ 12 volts. This is a good charge rate for an ATV. If you can pull start the bike and run it at a decent speed for a hour or two that should be enough to give a good charge as well. There is a small charger that is made by Battery Tender that will work great with out overcharging. Since you know the cause of the discharge you probably don't need to take a trip to the dealer.