Batboard

What is the A-B switch on the bottom of an Impres charger?

From the manual:

"The charger may cause a clicking sound in the receiving radio, caused by the periodic discharge pulses. If these clicks are objectional, changing the switch from A to B reduces the frequency of the discharge pulses, and has little effect on the charger. "

Basiccly it is the same concept as the switch on smartribs.
Just changes the clock frequency to stop interfering noise.