Mysterious exploding battery

[JuNK512G]

Enquiring on behalf of fellow club member. His traveller had a suspected blown head gasket or valve, carried out compression tests which flattened somewhat the seven year old Halfords battery, refitted the plugs & attempted restart, suddenly the battery exploded causing a complete end to blow out, acid everywhere. The terminals were tight so no spark there or anywhere else that we can think of. Can only assume an internal battery short, any ideas please as I've never heard of a battery exploding in that manner before ?

[kennatt]

I take it that you recharged the battery after flattening it,probably still gassing off hydrogen from the recharge,then bang.

[bmcecosse]

Maybe it was a 'pressure' explosion rather than a 'flammable' explosion due to build up of gas from the intense use - that couldn't escape because of a blocked vent. The important thing is to flush with plenty of water, and then neutralise with a mild alkali such as sodium bi-carbonate.

[Trickydicky]

Hope you are ok and didn't get burnt from the acid. Can only think it was a build up of gas as mentioned earlier.

[dalebrignall]

the batttery was not recharged it was running down , nobody got hurt but very strange .

[aupickup]

i have heard of batterys exploding when charging

[bmcecosse]

The battery will 'gas' when being heavily discharged... But a compression test shouldn't make great demands on the battery....the engine should be hot, so relatively easy to turn - and all spark plugs removed..... Was it, and were they ?

[JuNK512G]

Maybe it was a 'pressure' explosion rather than a 'flammable' explosion due to build up of gas from the intense use - that couldn't escape because of a blocked vent. The important thing is to flush with plenty of water, and then neutralise with a mild alkali such as sodium bi-carbonate.

This sounds to me to be the most logical explanation. Thank you all for the input, I will pass it on to my friend.

[JuNK512G]

I take it that you recharged the battery after flattening it,probably still gassing off hydrogen from the recharge,then bang.

No, this happened immediately after compression testing with just enough power left to activate the starter.

[JuNK512G]

The battery will 'gas' when being heavily discharged... But a compression test shouldn't make great demands on the battery....the engine should be hot, so relatively easy to turn - and all spark plugs removed..... Was it, and were they ?

I expect it was cold as the car had broken down the day before, plugs were removed. My own experience of repeated compression tests does hammer an old battery.

[rayofleamington]

refitted the plugs & attempted restart

From the description it was the 'trying to start' with a run down battery that makes me think of a blocked vent. I've not come across a blocked vent myself but anything is possible.

If engine does turn over you get an initial big current spike which then reduces as the starter motor speeds up.
If the starter motor isn't spinning - you get max current continuosuly (not a good thing!) and the current is limited only by the motor windings (which heat up quickly due to the current!).
Assuming this caused the battery to gas-off again, the pressure can pop a battery spraying acid etc..

[CDYMOGGY]

My dad had a halfords battery explode in his traveller as well, he was however under the bonnet when it went! That was also on start up, he must have used the solenoid push button to start. He had a big coat on and a hat on which covered him up. Still got the coat and hat somewhere bearing the holes from the acid... I've kinda been weary of batteries exploding ever since.