GB I have not gone over 16.8 But trying the 18v tool packs if you can find a way to attach them is certainly something I would not be afraid to try.

The cheap starters the one with the hard yellow plastic switch housing and a yellow plastic button has a much smaller contacts than either the heavyduty hobbico or the sullivan (the ones with the flexible rubber over the contact plates.

The switch is more likely than anything to give up and the way it fails is simply pushing the switch and the motor runs but keeps on running when you let go. The little contactor just welds itself together. This happened on the one with 5000 batterys and the setup that could potentially pull the most current. Adding a nine dollor tractor press start, starter switch solved that problem.

John