1974 Duster total electrical failure, followed by quick recovery.

I have had this happen with an Optima red battery. Engine dies...going down a hill. Bat voltage after coasting to a stop was about 7v. A few hours later, it was back to ~12v. The bat shorted internally, & then recovered. No more Optimas for me. I checked on the web & there many similar failures after production shifted to Mexico.