Help with Electrical Gremlin

I learned my Optima 'lesson' a few years ago. New Optima red, about 18m old. Going down a hill, engine died, no warning. Pulled over, batt was down to about 7v. This was NOT a charging problem. After sitting for a few hrs, bat voltage came back up to 12v. Bat was under warranty, but Optima would not replace it because 'it tested ok'. I no longer use Optima. I was very lucky because when the engine died, I was going down a steep hill & car had power brakes.