[mrlmd1]

Go to WalMart or any local discount auto parts store and get a 1.5-2 amp charger. You don't need anything fancy. A higher amp charger can burn out the battery as these are much smaller and lower capacity compared to a car battery and best to charge slower. Mine, a Schumacher fully automatic battery charger maintainer with float-mode monitoring, I think was less than $30 out the door.
Most of these come with spring clips (alligator clamps) that can attach to the battery, and also with a flat 2 pole connector on the end (the alligator clip end plugs into this). Open the box and look at the wires. If it's not in the box with the battery charger, get a mating flat 2 pole connector which attaches to the battery terminals permanently, and leave it hanging on a short lead under the right side battery cover out of the weather but where it is accessible, so that if you ever have to charge it up again, you can just attach the charger without taking off the side cover over the battery and trying to reach the terminals. Just make sure the polarity hookup is correct. You can also use this flat connector off the battery to supply 12v to some small accessory, like to recharge a cellphone or power a GPS, nothing big or you won't keep up with the bike's charging system.