We use Auto Meters BUSPRO-660. It charges 6 batteries independently of each other at the same time and has indication lights for charge levels as well as if the charger detects problems with any of the batteries. The charger will adjust voltage/current once batteries are charged and will maintain a full charge on all of the batteries.
Here is a link to the product page.
http://www.autometer.com/6-station-a...-115v-agm.html
We also created a battery cart designed specifically for this charger with the charger mounted vertically. The cart hold 10 batteries (6 charging and 4 storage) and has wheels for easy transportation to events