Click>>>BOOM...yes Virginia, batteries can and do explode! Audi Content!

Steve Eiche seiche at
Wed Sep 3 10:29:52 EDT 2003

FWIW, I have seen this happen in a '90 100q with the battery under the
seat.  When the owner went to start the car, she "heard a large boom and
smelled something funny" behind her and the car would not start.  The
car was then left for a week until it was towed to a shop. Mistake...

What a mess.  The entire top of the battery had blown off (proper
fitment for the car BTW, but couldn't tell in the aftermath if the vent
had been connected or not).  The acid then leaked onto the floor,
destroying part of the wiring harness and thoroughly soaked the carpet
padding and sound deadening.  The seat foam was burned and the parts of
the top of the battery had stuck to it.  Nothing was visible until the
seat was pulled up.


Very, very strange, Peter!

Battery water is decomposed into H2 and O2 only when the battery is being
overcharged, normal charging of a partially discharged battery does not
cause this H2O breakdown.  Only a faulty regulator can cause this condition
with a good battery.  If the battery had a shorted cell, a good regulator
would overcharge the remaining good cells in attempting to establish the
correct battery voltage.  The battery is toast, but have the regulator

In either case, the resultant mixture of H2 and O2 would be forced from the
battery vents during and immediately after the overcharge condition.  This
stoichiometric mixture discharged from the battery vents, with the motor
running at a reasonable charging speed, will be immediately diluted to below
the LEL (lower explosion limit) by under the hood air movement.  When the
engine is stopped there may be a momentaary build up, but the source is
eliminated when the engine is idling or stopped and further, the mixture is
lighter than air.

The individual vent hole in each cap is designed to be too small to allow
flame propagation, and the Audi type vent tube is too long to allow similar
flame propagation.  So IMO, unless some caps were inadverntly left off, and
the required explosive mixture conditions established within the battery air
space, and an ignition source established at the vent, there could be no
explosition.  The only open ignition source might be the rotor to cap spark
gap, but if an explosive mixture existed at that point the cap would have
been removed.

 >> From: Peter Schulz <peschulz at>
 >> Date: Tue, 02 Sep 2003 13:43:48 -0400
 >> To: 200q20v at, 20v <audi20v at>,
s-car-list at
 >> Subject: Click>>>BOOM...yes Virginia, batteries can and do explode! NAC
 >> And I thought this only happened to other people...
 >> Patient was a 1992 Infiniti G20 owned by a friend of my wife's.
 >> She went to leave our house, turned the ignition key which was
followed by a
 >> loud BOOM and smoke from under the hood.
 >> I opened the hood to find the vent caps missing from the battery,
the top of
 >> the case cracked open and the stench of sulphur.
 >> If it had not been for the "over the case" battery clamp, the whole
top would
 >> surely have blown off.
 >> The battery was a Nissan oem battery, After I liberally washed the
area around
 >> the battery with baking soda and water, we were able to find a
replacement at
 >> a nearby Autozone...
 >> I shudder to think what might have happened if this battery had been
under the
 >> rear seat, as in one of my Avants.

There is no ignition source at this location.


 >> I assume what happened is that the water level was too low, and that the
 >> turning of the ignition switch caused an internal short that ignited the
 >> hydrogen?
 >> More reason to periodically check the water level in you batteries.
 >> -Peter

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