It blowed-up real good. It only took two damaged batteries and one that blew up for me to figure out, with a lot of help from others, what likely happened.

2022 Bought a battery. Everything was fine until I left a light on and the battery went flat. I hooked it up to my tender and it wouldn't take a charge. I took the battery back and it was out of warranty, so I bought another. Everything was fine with that battery.

2023 Another light left on. Took the battery to the shop and they were able to revive it. I hooked it up and the car started fine, hooked it to the tender, and it wouldn't start the next day. They put it through a load test and you can hear it producing prodigious amounts of hydrogen gas, and oxygen. They replace the battery, I put it in the car, the car starts right up, and I park it for the winter with the CTEK charger on it. The lights show it was nearly fully charged, so I left it to do it's thing.

Sometime shortly after I put it away for the winter I noted what appeared to be antifreeze on the floor and thought, "That'll keep until spring."

I needed to get the Mark II out of the way to get something else out of the storage building. I unplugged the charger, sat in the car, put it in neutral, turned the key, nothing. Nothing at all. No dash lighting and no headlights? I popped the hood and wasn't sure what I was seeing, because the battery was hidden from my view by the gigantic oil bath air cleaner. The I shined a light on the battery I saw the top half of the battery gone. I noticed a stain on the hood liner. I looked right into the half-empty acid chambers and saw a cataclysmic scene I never hope to see again. I'm just fortunate no one was around, and I'm fortunate the hood was closed. There was white acid residue that had done its damage months before. Everything it touched that was plated isn't, anymore. Zinc and pot-metal parts have severe etching, as do all of the aluminum parts. Anything I had painted with Rustoleum was nearly bare of paint. The Jet Coat exhaust manifold resists heat, but not acid. The powder-coated parts look just fine.

The battery has the worst ingress and egress I've ever seen. When it blew it spewed foreword into the back of the carb and the area under the air cleaner. The acid then ran down the back of the engine, spreading out over the aluminum bell-housing and cascading over the iron transmission. I reported the incident to Hagerty. They wanted a copy of the receipt for the battery. I went to a knowledgable group on the Vortex and asked them to explain to me what happened.

It turns out I likely had no "bad" batteries, only marginally good ones. I'm convinced that, in all cases of failure and eventual hydrogen gas explosion, the charger was the culprit. It was brought my attention that all 3 batteries could have come from the same pallet in the dealer's warehouse. It appears that they all had a weak cell and it was detected as needing more charging. The tender started boiling out the single battery compartment that contained a negative and positive terminals. It appears that the fluid got so low that it exposed the defective plates and the third element of an explosion became available, ignition.

The only thing that I can see that's unscathed is the 1994 blue paint job. I believe it was lacquer. Several people that have looked at the damage say that the engine must come out to get to the rest of the firewall that's been cleaned and neutralized, but everything steel flash rusted. The front of the engine is just fine as the air cleaner blocked the spray. I've asked Hagerty that they ship the car to Rick Payton in Wisconsin, a former Mark II owner and lover. His shop produces some serious prize-winning Cadillacs that all pass muster. It won't be in better hands, if this all works out.

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