I had a feeling that it would be a loose ground once you described your symptoms. I check all my ground on a bi-weekly basis as I have had this happen to me during a night trip and was in panic mode until i realized it was a loose ground. that i didnt tighten up from the day priors repairs.

 

It was that ground. I am going to have to come up with something better. Maybe see if I can pull the grill and tack a 1/4" nut up under the hole for the hold-down. Maybe then my hold-down would hold the battery in place as well. I have to keep something over the side of the front battery to keep it from working over and arcing on the fender.

When I put new batteries and cables in, the ground post is going toward fender.

I didn't put these in this way.

 

Any hardware store will have nuts on a tin clip that will go onto a piece of sheet metal, like the edge of the fender. A regular machine screw or bolt can then be tightened to full torque without a wrench on the nut.