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

Bernie Benz b.benz at
Tue Sep 2 21:25:24 EDT 2003

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
> Peter Schulz
> 1990 CQ (awaiting S2 3b engine transplant)
> 1991 200 20v TQW indigo mica
> 1991 200 20v TQW titanium grey
> Chelmsford, MA USA
> peter at

More information about the 200q20v mailing list