Hello Bill,
Use #OO welding Cable, it is flexible, stranded,
oil resistant and will keep the IR (Ohm's law E (voltage) = I (current) X R (resistance) loss to a minimum. The only down side is to find a buddy with a large cable crimper. I also put a shrink wrap sleeve on the wire to mark the positive and negative for identification down the road.
It is cheap and available at your local auto parts store. The stiffer single strand solid stuff is difficcult to use. The welding cable has a good abrasion and
oil resistant insulation on it.
Tony R.