Can you use a plug adaptor with battery charger?

If you're using the same input voltage, as the battery charger was designed for, then a simple socket adapter will make absolutely no difference to it's function.

On the other hand, using a different input voltage to that which the battery charger was designed for, will make a considerable difference to the output voltage and current.

Hence a 120 V automotive battery charger, if plugged into a 220 V socket will deliver nearly 24 V to a battery instead of 12 V, although the current supplied will be half it's normal value.