Yup, nicad. You could run out and get a nimh, lion, or lipoly, but the ignition is 4.8 nominal. Not 5, not 6, not 7.2. Might as well get something inexpensive that works well. By the time you added regulators with lions and lipolys there would not be any weight savings. Hard to mess up a nicad, too.

You will probably use a DSC super switch with standard radio connectors on it. Makes charging the ignition battery real easy and they are generally great switches. There will only be one end of the ignition wiring that will need to have a plug. Grab an old servo extension and cut it in the middle. Solder splice the end onto the ignition wiring that you will need. Don't forget to put the heat shrink on before you solder the wires together. Red is still positive between the switch, the ignition, and the cut servo pigtail. DO NOT get them backwards.