Usually voltage is around 13.8 DC and a battery charger doesn't have a capacitor... I would say this matters but if your clock is the mechanical clock, really all that matters is you hook the (+) to (+)and (-) to (-) and voltage is around 12V. The reason is the voltage just sort of "winds" a spring that keeps the clock going. You can hear the louder tick every so often in the clock, that's the winding. I've found though that mine keeps time differently depending on the weather, in the cold it's slower and in the warm it's slow, but not as slow!