If there's no load on them (no battery connected) then they're not outputting any amperage at all.
Current is measured inline with a load, no load, no current.
A fairly good explanation here:
As for the voltage, it depends on the battery. Generally 48V batteries are 13 or 14 cells in series. 13 cells is usually around 54V fully charged, 14 cells is around 58V. Alot of 14S batteries are labelled/marketed as 52V, but not all.
It sounds like you have some chargers at each voltage, it would be good to determine which one is the correct one for your particular battery to avoid over charging it.