I picked up a Battery Tender Junior for my People S 125 scooter and it does a great job for under $30....
I use a regular Battery Tender but the junior will work just fine too. In the fall I remove the batteries from my bikes, bring them inside, and clean the terminals with a battery cleaner (I use Permatex). Since I have one charger and three batteries, most of the time the batteries just sit on a bench not connected to anything. Once a month I top off each one with the battery tender, one at a time. In the spring I top off the battery one last time, apply corrosion preventative to the terminals and put it in the bike.
Not all chargers should be connected all the time but the Battery Tender can be used this way if you want to do that.
Dale B