Power= Voltage x amps so to make the same power a 6 volt neeeds twice the amps of a 12 volt. As current runs ON a wire not in it, is is the surface area that is important, and clean tight bounds. The other thing is consider investing in an electronic ignition, lot easier and more reliable than conventional. So saying Katy my 6 volt WC54 started on convetional, despite being set 22 before TDC! You can jump start from 12 volt BUT turn all lights off and just touch the jump leads, as soon as it fires take away! The new type gel battreies are amazing and hold charge for a long time, but are ***** expensive. I have a standard 6 volt lead acid which works fine.