In the event you need to put your M12 or M18 battery on the charger, could you just swap it for the other type? In short, M12 ...

This charger unlocks the capability of bulk overnight charging on a single 15A circuit and rapid daytime charging while going ...

you can get the M12 and M18 Super Charger, which accommodates one slot for each battery type. However, this super charger only charges one battery at a time even if you have two attached.