Caroline's Truck had listed 12 volt @ 2amps and 12 volt @ 6 amps in response to my question. Didn't know if that meant I could use a 12 volt charger at the lower amps on the 6-volt battery.
I do have a 12-volt charger, but only at 2amps, 10amps and 50amps.
I also have a 6-volt at 1amp which isn't strong enough.