You lightly solder 2 wires to the proper terminals of the box where the batteries sit..............you attach alligator clips(an actual plug end is better) to the ends.....one red(positive),one black(ground). You then find any power source(Radio Shack has universal ones with adjustable outputs and voltages) that plugs into the wall and is greater than 200 MAmp and up to 1000 Mamps, and connect it positive to positive,negative to negative. I keep a timer here that I can set for 6-8 hrs.charging on my lawnmower battery. 6-8 hrs. is a good charge time for most Ni-Cads.