<VV> Battery Explosion

[FrankCB]

Bill,
      It sounds like it was an INTERNAL explosion inside the battery cell.  When the electric charge from the battery charger finishes with the chemical reactions involved in recharging the battery, the excess electric current goes into decomposing the water part of the electrolyte.  This produces not only hydrogen, but also OXYGEN (H2O, remember).  The mix of hydrogen and oxygen together in the cell is extremely explosive and merely requires an internal spark above the liquid level to ignite.  The large drain of current to the starter probably caused an internal short and the resulting spark was the ignition for your explosion.
     This is why it's important NOT to overcharge a lead acid battery, especially an old one..
     Glad you suffered no personal injury.  Cars are much easier to repair than PEOPLE!!!
     Frank Burkhard

In a message dated 09/26/09 16:07:46 Eastern Daylight Time, whubbell at cox.net writes:
I don't think it was Hydrogen gas.  My car is Factory Stock Restored (well, 
it was before this incident anyway) so the battery had the special vented 
caps with hoses that vent the hydrogen gas outside the engine compartment. 

It looks like the explosion occurred in the center cell on the positive 
side.  I suppose it could have been hydrogen in the battery which blew it 
apart, but the ignition source was inside the battery, and therefore was 
probably some sort of internal short.  It only happened when I hit the 
starter switch, which would of course cause a large current draw from the 
battery.  There is no evidence of other electrical damage, so I do believe 
the ignition came from within the battery itself.