A little more battery info-
A battery will lose 1% of its charge per day just sitting there doing nothing. Trickle charge the battery at least once a month if the bike is not ridden. Most motorcycle batteries only last 2 to 3 years.
I have found that it is best to use a 1 Amp or smaller trickle charger. Most motorcycle batteries are small and just can’t take a high rate of charge.
When you start the engine, you need to have the engine faster than idle for at least half an hour, to get the battery charge back to where it was before starting the engine.
most of this is from http://www.dansmc.com/batteries.htm