Man, do you know how lucky you are to have a tech that knows what he is doing and actually cares? And the fact that he is a Volt owner is an added bonus. You are also lucky that the dealership let you talk directly with him....because my experience has been they don't want you to get "chatty" with the techs...they think you are wasting their time.Just got my car back! Unfortunately I work a fair distance from home, the dealer was near work, and the car I've been driving belongs to my mother, so I had to put my car in the garage at work for the weekend until someone can take me to pick it up.
It turns out the root case was a bad Battery Energy Control Module as I had suspected. The tech started performing the service bulletin regarding the faulty BECMs that my model year suffered from, and when he took the cover off the battery to install the new module, he found pooling coolant inside and had to order a new battery.
I actually got to meet the tech when I picked the car up, and he was super interested in showing me the old battery and explaining what happened. He's a Volt owner himself and he said he's fixed a ton of bad BECMs, but has never seen coolant inside a battery, which is likely due to faulty workmanship from a past service visit.
So glad you are back in business again. Fingers crossed, my 2017 with just under 30,000 has been perfect.