DC Ground Fault on Battery Charger when Batteries Disconnected

Unplug it before disconnecting the load.

Or, look on-line for trouble shooting instructions for your particular unit.

Or buy a new one.

It is not necessary to plug negative terminal to ground because when your positive terminal touches any metal your breaker will trip. You can get a ground in positive or negative terminal and your earth fault will indicated + or -. Check installation manual. Regards.

Typically the open circuit battery charger's charging output potential available at its terminals is much higher than the battery terminal voltage. This voltage level will be clamped down to a lower voltage level as determined by the battery condition upon connection or when it is charging.

When you disconnect the battery without turning off the charger, your motor protection circuit will sense the sudden voltage rise in voltage brought about by the open circuit voltage output of the battery charger. This rise in voltage will be sensed and maybe interpreted as an unbalanced current by the protection circuit thereby triggering a faulty condition?

This false condition maybe solved by initially turning off the charger before removing or opening any battery connections?

there are protection relays which provides trip when there is no source supply. read relay broucher for details