How about charging the KR808? Can I charge it in the 901 charger, or do I have to get a charger for the KR808?
The charger works on voltage. It looks to see how much voltage the battery provides. If its below a certain level the charger decides to charge the battery. Then it watches and looks for a higher voltage. As the battery charges the voltage goes up. Once its high enough the charger shuts off.
The only difference between a m40x and 510 and 901 and KR808D-1 charger is the
threads. Since the 901 and 808 have the same
threads they can be charged on either charger.
In fact there are USB style (never saw a plug into the wall this way) that doesn't have a screw in socket on the charger but a fancy silicon type sleeve thing. It grips the side of the battery and has a sprung center connection. It can charge all the
batteries I mentioned above. But since it isn't threads but the silicon sleeve it doesn't hold the battery very firmly and can be very finicky to use.