· Super Moderator
2012 Std w Nav
wildass guess but the place to START looking for a solution is probably battery coolant circumator pump or battery heater or the three-way valve that connects them. I don't know if the car is smart enough to run coolant through the coolant radiator that's near the engine radiator to warm the coolant in case of failure, but that'd go a long way to explaining why the battery BECOMES fine after a long drive on ICE. For example, the coolant heater failed so car switches 3-way to postition C on the diagram The Chevrolet Volt Cooling/Heating Systems Explained , runs the engine and hopes for the best.