Motorcycle batteries have one thing in common, they are all too small. Even the biggest ones are too small for what they have to do. These days, it seems as though nobody believes in kick starters anymore, so a well taken care of battery is doubly important.
A battery will loose 1% of its charge per day just sitting there doing nothing. So you can see that you just can’t park it, walk away, and come back in 4 or 5 months and expect it to work. Amazingly some of them do work after that kind of abuse, but a greater number of them don’t. The cure? Trickle charge the battery at least once a month.
You can also use a maintenance type battery charger. This type of charger has electronic circuits that can detect when a battery is fully charged and cut the charging rate. When the battery charge goes down the maintenance charger senses it and starts charging again. This works very well.
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 the high rate of charge that a 6 or 10 Amp charger gives. A general rule of thumb is that a battery should not be charged at more than 1/10 its rated amp capacity. As you can see, even a big motorcycle battery is maxed out by a 2 Amp charger.
Most of our Batteries are lead/acid types. With this type, the Battery should be charged till it is gassing (bubbling) freely, but then stop, don’t boil all your water out! The temperature of a battery must not go over 112 degrees. If it does, the battery may be ruined. If the Battery gets hot during charging you are using a charger that has too high of amp rating. Change to a less powerful charger or stop charging and let it cool down.
Excerpt from “http://www.dansmc.com/batteries.htm”