Well, its about that time of year to put the Z away for the winter.  It has been sitting in the garage for a couple of weeks and it is around 40 here today.  Turned the key and got nothing.  I am not too surprised since the battery is pretty old and its cold this morning.  No big deal, right?  So I put it on the battery charger for 2 hours.  When I turned the key to try it, I immediately heard a really loud pop and vapors came out from under the hood.  I was really shocked to see that my battery had exploded!!

Not only did it blow the cap off, it blew a big chunk out of the top and broke out one whole corner of the top portion.  The explosion was so powerful, that it put a bend in the battery hold down frame.

Luckily, had the battery access door closed at the time and the acid only hit the underside of the access door, instead of spraying all over my paint.

Anyone have an idea of what would cause the battery to explode?  I have never had this happen before.

 

Marty 

Just happened to have a friend who had a battery explode with long term storage hot storage with a trickly charger on it. He heard that old batterys have an issue with plates that warp, then eventually touch and go BOOM.

Sounds like you got generally lucky. Good lesson about aging batteries.

Edited November 3, 20177 yr by zKars

 The electrolyte in a charging battery breaks down and emits Hyd. gas. Likely the closed battery access flap and a closed hood allowed the gas to accumulate under the hood until there was a spark under the hood. I blew up a 12v battery in a generator welder some years ago. The battery was enclosed but somehow a spark from my welding found it's way inside. The result sounded much like yours. Time to break out the baking soda and water.

I had the hood and battery door open the whole time I was charging it.  Only closed it to start the car.  Could gases build up that fast?

 

Is there an Optima battery that is an exact fit in a 240Z??

Learned something new. zKars is correct about plates warping in old batterys. It happens when the electrolyte level drops below the tops of the plates leaving room for hydrogen gas at the top. The vibration of starting the engine probably caused the warped plates to get close enough to each other to cause a spark.

Hydrogen is explosive at very low concentrations and doesn't take much to ignite.  There's some good reading out there about it, I posted one below. 

I had a friend check the electrolyte level of somebody's battery with a lighter.  The gases lit up in his face.  They threw him in another car and drove over a couple of curbs to get to the water hose at the gas station to rinse his face off.  That was back when water and air were free.  It was Saturday night, cruising night, at the shopping center parking lot.  The old days, when we didn't have "phones" to keep us occupied.

https://www.nasa.gov/pdf/513855main_ASK_41s_explosive.pdf

A battery I had in my first 240Z, a '71, developed a loose battery post internally.  When I first saw this thread I thought maybe someone's battery post had gotten loose and maybe that would have caused a spark with current flow.

Edited November 4, 20177 yr by Mikes Z car
grammar improvement. My english teacher would be proud.