One of the cool things I've read about on the net, but never actually seen, is a device to test your battery charger. I cannot seem to figure out how they'd work. I mean, they have to present a resistance (mimicking the internal resistance of a battery), as low as in the 10s or 1s of mohms while having a voltage across them mirroring the battery you want to charge.

Now maybe I'm overestimating the amazing nature of these things but without data I can only guess, so how does a battery charger tester work?

Thanks!

 

device to test your battery charger

What battery chemistry are you referring to?

 

Li-Ion or Ni-Mh. 3.7v or 1.5v respectively (that's the nominal charged voltage, of course).