Wife and I took the 914 to a cars and coffee (about 20 miles away) yesterday morning. Everything seemed normal except that we started noticing a strange odor on the way home. Just a few blocks from home the engine quit. I managed to get it running, although poorly and got it home. The first thing I checked was the battery. The case was bulging and too hot to handle. It was also outgassing vapor. This is a one-year-old AGM battery.

I got it exchanged for a new one at no cost to me but the experience was unnerving.

I suppose that I now have to be certain that my charging system did not contribute to or cause this battery failure.

Has anyone experienced this sort of battery failure? It must have been some internal short to have such a rapid decline. I really was concerned that the battery would rupture.

The chemical vapors left a coating all over the engine compartment/trunk area. Are there any good ways to neutralize the acid residue?

Thanks.

What battery? My experience with batteries over the last few years has not been good. Not the same as yours but I don't get more than three years out of them anymore. Duracell AGM from a shopping club.

There is likely a baking soda solution you could buy buy you could also make some up. I would really be concerned about what was left behind. That stuff has killed so many 914's we cant count them all. Your alternator or voltage regulator is likely fried check all the wiring for overheating as well. Maybe the grommets through the rear engine tin is missing causing a short. Glad you stopped.in time to save the car.

I made a solution of household ammonia and water and wiped the area down. My thinking is that ammonia is alkaline which should neutralize the acid residue. But maybe my recall of chem is faulty. Way back when I was a kid working at a gas station, the old hands would pour coca cola on corroded battery trays and it worked somehow. Coke contains phosphoric acid, so it is a mystery.

I'll checkout the wiring and bulkhead passthrough's for shorts. My battery is actually in the trunk and not in the normal 914 location. Next will be a baking soda wash. Then clean and apply rust reformer and paint. I hope the alternator/VR are OK.

My plan is to check the wiring, install the new battery, start it up and check the gauges for abnormalities and the exposed wiring for heat.
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I would suggest that the VR has failed and the battery has overcharged, the OP is lucky the battery didn't blow ,up appears it was close to it .
Not likely the battery was faulty so a full cleanup is required in the enginebay followed by a test to check input voltage @ the battery , don't proceed further if the voltage is over 14.4V (no load) .
Don't continue using the car till you have tested otherwise you may have a repeat issue with a possible worse outcome ,good luck and report back, cheers.

Do you mind sharing the brand of battery?

Have you measured voltage when running?

Was thinking the same. Odyssey batteries in my Bug and 914 are 7 and 6 years old. Battery in my airplane was 11 years old and finally started to exhibit low voltage. Would think any decent battery would last 6+ years.

It was a Duralast Platinum AGM in the H5 size.

Not yet, but I will when I finish the cleanup.

Just a bit OT, but lately the only way I get decent life from batteries is to have all my vehicles on maintainer-chargers in the garage. Between older cars that sit for weeks and newer cars that have constant drain from digital stuff, batteries just run down too fast.

Yup, anything that sits for more than a couple weeks is plugged in.

Good move not an easy task but you will get there ,cheers.

Here is an update:
The cleanup is finished and I temporarily installed the new battery to see what I've got and begin troubleshooting. My engine is twin plug crank fired and uses Electromotive HPX modules. One of them is inop now and these units are no longer produced. Additionally, my tach is fried so there must have been some voltage spike that took out those devices.

Most probably my voltage regulator/alternator caused the problem. I don't know how a battery failing, even with an internal short could generate anything above the design voltage.

So now my immediate search is for a functioning Electromotive HPX that I can acquire. And an 8000 RPM tach. If anyone has either of these available, please contact me. Alternately, I will replace the entire ignition system. I want to stay crank-fired and twin plug. What are the options?

Last comment/question. Is it possible to pull the alternator on a 914/6 with the engine in the car? I do have an access hole in the firewall. Is there enough room to side the fan module forward to clear the engine shroud and then up and out?

There's a great old school speedo shop in North Park-- Foreign Speedo, should be able to check/fix the tach
Foreign Speedo (619) 298-5278
2246 1/2 University Ave San Diego