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MG MGB Technical - Exploding Battery

On driving to work yesterday I heard a bang underneath the car, checking in the rear view mirror I saw nothing bouncing around in the road so continued on my way. Coming home was no problem and also when using the car in the evening. However next morning the car stuttered on starting but it did start OK. Driving the car out of the garage I noticed a puddle of water (or I should say battery acid) on the floor.

On investigating I found that the end wall of the battery was blown out and split all along the top and down both sides. The bang was obviously the battery exploding.

The battery was about 4 years old and has never showed signs of a problem and was replaced because the previous battery also exploded in the same way. I had the car tested at the time by an auto electrician and they found no faults with the charging system - but I had the alternator changed as a precaution.

Having 2 batteries going the same way indicates there must be a problem somewhere but where? Does anyone have any idea why this is happening?

The car is a 1975 MGB.
Gary Wemyss

Gary,
Is there any sign of a short? I'm thinking if the + side of the battery was able to contact ground it could spark and potentially set off an explosion.

Paul
PR Peterson

The battery compartment must be vented to the atmosphere.

Other than that --- ?????
Dan Robinson

There is no obvious sign of a short but seeing that the battery compartment is not much bigger than the battery could the battery rock and short the +ve clamp to the body?

As there is no battery clamp in my car this could be the explaination!
Gary Wemyss

Putting your new battery in one of the plastic battery bins will insulate the battery and clamps and keep it tightly in place. Should solve the problem!

(Exploding batteries! Ouch!)
Kim de B

Years ago one of my work coleagues had a beat up Chevrolet Impala. He hit a pothole and smoke started pouring out of the front corner of the car.

He had no battery hold down clamp and the battery terminals were on the front side of the battery. When he hit the hole, the battery slid forward and the terminal(s) contacted the radiator support and boom!

He came back to the office with a new battery held in with a bunch of bungie cords.

Good Luck
PR Peterson

Gary,
Your battery probably had an interal short that caused a hot spot or spark that inignited the hydrogen/oxygen mixture above the plates. Very rare but not unheard of.
Leland Bradley

But twice? It sounds more likely the battery shorted on something. Perhaps on the chassis.
Steve Simmons

Gary
If your battery is exposed to dirty conditions the vents in the caps could have become plugged and caused a gas buildup causing a boom. Some caps go on very tight. Also if your fluid in the battery runs below the plates could have some effect. Old Volks Wagens had a reputation for catching fire when fat people sat on the back seat over the battery box without the safety cover on the battery. So make sure the battery is tied down good.(I'm not saying you are fat!) Mark
MLS Somers

If you don't have clamps then it quite possibly did bounce around and short out, or just break up after being unsecured for 4 years. I wouldn't advise the battery bins, you have to cut holes in them for the clamps or leave them bouncing around and insulate the underside of the battery cover as the terminals are that much higher, the weight of the battery is taken on the lip of the box, and it seals in explosive and corrosive gases.

"I'm not saying you are fat" - but are you saying he is so tall he has to sit on the back seat to drive?
Paul Hunt

Aren't missing or ineffective battery clamps an MOT failure point ?
Miles Banister

Unless they can tell from looking underneath I am not aware that they remove the battery cover to check. Can't see anything in either reference source I use relating to battery security, the nearest being "Components secured with, for example, rope are not acceptable"
Paul Hunt

The Brit Gov't doesn't want you holding your cars together with rope? How 'bout that...
Wade K

Hi all.

I seem to recall that a cell whose electrolyte has frozen can behave in exciting ways, and I guess that an end cell is the most likely to suffer.. was the battery exposed to well-sub-zero temperatures ?.

Don
Don

The German TÜV have failed my MGB for not having the battery tied down properly in the past and they did't take the cover off. (They've also missed it a couple of times too!)

Mike
Mike Standring

My midget has just had it's MOT, and it failed (apparently sticky kingpin). The test centre has made no reference to the battery, which has no clamp, so it seems that the MOT does not test this.

oh, and when they were fixing the horn - they collapsed the collapsable steering column. anyone know who's liable for what as neither of us will admit that we broke it.
Andrew Hazon

Several years ago there was a well documented fatality on the motorway in the UK where an unfortunate rolled his GT, was trapped inverted in the wreckage, and the unsecured battery contacted the metal cover and ignited the lot.
An unsecured battery can kill you, so screw it down now.
Paul is absolutely right about the bins. Batteries don't need wrapping in cotton wool. Consider what it's like living with the engine. The bins will only serve to retain more explosive gas. Duh!
I've only had one battery explode - luckily it was on the forecourt of a battery retailer %). That was in a Midget where it's impossible to check the levels or top the damn thing up, so it ran dry then went BANG.
Dave
D Wellings 1

Never heard of a sticky kingpin causing an MOT failure, sloppy i.e. free play yes.

Did they work on the horn? Or did they refuse to do it because the column was already collapsed? If the former then you probably have a case. If not then you would have to prove that it was OK when you left it with them - difficult.
Paul Hunt

Hi all.

I did a little digging, and found several web sites stating that charging a frozen lead acid battery can cause an explosion. If the car had to be jump started that day this might indicate that the battery was frozen at the time.

Freezing can also cause cracking of the battery case due to expansion.

HTH.. Don
Don

So far, I like Don's frozen battery theory perhaps causing a split in the casing itself causing the leak. But this does not explain the "bang" that Gary heard under his car?

Kim, keep in mind that normal charging of batteries cause off-gassing of hydrogen as Paul suggests. If the metal bin cover seals tightly over the bin opening then perhaps you could see enough hydrogen build up to cause a problem if an unintentional spark were produced. Same problem with batteries in sealed boots! In this case the original design (same on MGA) may be best for both security, and ventilation.

Regards,

L.C. '74 B/GT (with group 26 without plastic bin)
Larry C.

Hi all.

This is speculation, but if the electrolyte level dropped significantly due to a cracked case the charge capacity of that cell would be reduced. If the cells capacity was reduced significantly, that cell would be unable to accept a normal charge current, resulting in heavy gassing, overheating or even boiling, potentially resulting in an explosion.
I have personally seen an instance of a battery with very low electrolyte levels becoming hot when charged at normal charging rate.

Another possibility is that the case cracked between cells, resulting in the electrolytes of two adjoining cells coming into contact with each other, effectively shorting one cell, again potentially resulting in an explosion.

Don
Don

Since a cell wih no electrolyte in at all won't pass any current at all whether charging or discharging, I would have thought that low level of electrolyte would have reduced current flow and hence any gassing. But even then a spark would still be required to ignite any gasses. If the case cracked maybe the plates distorted and touched, which would cause a massive internal current and possobly arcing, or maybe the link broke creating a spark which did the igbition.
Paul Hunt

Hi all.

A cell with low electrolyte will behave normally BUT with lower capacity, so will reach full charge before the other cells, and subsequently begin to overcharge while the other cells are still happily accepting charge. The low electrolyte cell's voltage will rise, but not enough to reduce the charging current significantly (until it boils dry).

I agree that warped plates that touch (possibly due to heat) may provide a source of ignition.

HTH.. Don
Don

This thread was discussed between 14/02/2004 and 22/02/2004

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