I used a standard automotive charger to charge the SLA (sealed led acid)
batteries, however when using a large charger with small batteries it is
easy to over voltage the batteries which will cause them to out gas (very
bad). To prevent this I built a small circuit that monitors the battery
voltage and turn off the charger when 14.8 volts is reached.
Charger Schematic.sch (eagle V4.03 schematic)