Originally Posted by RonD
it could be corroded battery cables as well, either at the battery end or at the starter/engine ends, and they can corrode internally under the insulation.
+1 on corroded cables. They can cause all sorts of weirdness. I had an intermittent flashing O/D light, intermittent flashing Air Bag light, the Bluetooth would intermittently be unavailable, the starter didn’t sound right and was laboring to turn the engine over, and finally I’d randomly lose all power in the truck without warning (dead from nose to tail). The only thing that would reset it was disconnecting the battery for a couple of minutes. The battery and clamps were less than a year old and the alternator and started both tested out OK.
It wasn’t until I cut into the cables behind the battery clamps that I found corrosion under the insulation. Once I cleaned that up, she’s been perfect.