48V vs 24V why/why not?
Get a 12v lithium charger and plug it into the park''s power or a generator or a friends rig. Set the charger to a slightly higher(but safe) voltage than you regularly charge to. Connect to battery 1 - charge, when done, move to battery 2, repeat until done. If you create access in building you could do it without disconnecting the 48v battery.