Hi.
Have a couple of batteries for DeWalt drill, saws, that are dual voltage. How do they work ? Do they need a 'special' charger ? What senses to deliver 20 or 60V in/out ?

 

I would assume different available voltages would be on different pins. The tool will plug into the appropriate section of the battery. But that's just a guess. To get the advantage of all the voltage perhaps there's a circuit in the battery that delivers the necessary voltage to the appropriate pin while regulating the 60V down to 20V. But again, it's just a guess.