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At right is the basic circuit of how to hook up 2 cordless drills to charge a 12 volt battery. Notice that no switch is needed. This will be true as long as the reverse flow on the diode chosen is very low. Summary: A bicycle driven emergency battery charger can be made rather simply from two cordless permanent magnet drills and commonly available parts that will produce from 10 to 45 watts charging capacity. This can be used to charge 12 Volt storage batteries or a modified drill NiCad battery pack.

Take the cover off the battery pack that came with the drill and attaches a wire to each end of each cell without taking the series string apart. These wires are then run to the outside of the case. Then depending on the voltage needed to run the intended device one can tap off that voltage. The series string of cells is charged all at once by hooking the bicycle generator across the battery pack as a whole.

Offered by Mike.