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MG Midget and Sprite Technical - How do batteries die? (GMC)

How do batteries die? Or more specifically, what exactly wears out or gets used up or fails when they will no longer work?

The concept, of a cathode and an annode in a sulphuric acid electrolyte is pretty simple. As long as one keeps topping up any water lost in evaporation or as released hydrogen and oxygen, why won't they last more or less indefinately?


I have spent a good deal of time trying to understand the theory of batteries, and I still don't understand them, but apparently the cells sulphate over time, whatever that means.
I am sure an expert will be along in a minute.

Dave Barrow

I understand that when being charged, one plate (the cathode?) changes from Lead to Lead sulphate, at least on the surface, whilst the other stays as lead. The sulphate precipitates (?) out of the sulphuric acid, which becomes weaker. As it discharges this process is reversed.

There are "fixes" mentioned on that always truthfull internet thingy, about connecting a charger the wrong way round to "shake" the sulphate off the plates when a battery gets tired. Implying that the normal discharging process, of reversing the lead sulphate deposition and liberating electrons to start your car, doesn't work any more, though I don't know why.
But I more or less made that up!

I don't know the answer but the following may interest you and possibly expand or extend what you already know, I'll also see if I can find further notes (if I've kept them). (for some reason the BBS adds the s to this link so you'll need to copy and paste it).
Nigel Atkins

I think they go bad in multiple ways

I just went th ur this a few weeks back, I thought I had corrosion built up on my bat connectors ... which was but not overly bad from cleaning them 6 months prior and the bat came back for a week or so and got bad agian... left me stranded a few times

Finally I accepted that the bat (might) be bad and so I picked up a $15 battery at the auto
salvage yard and stuck it in AND WOOOOoooW ... MADE A HUGE difference

For me the bat died so slowly I had not realised how depleted it ran ... the bat was so bad and low it could barely keep up with basic operations even tho the gauge showed 14 volts... (I guess means it's charging 14 volts) not holding

But what goes bad? I'm not sure aside from sulifiding but that's because of them sitting undisturbed for long periods

I watched some one take a battery apart on youtube for the plates .. these things are bullet proof to get into its no small 5 minute project

But having purchased a used a $15 bqttry...ill nev r buy a new battrey agian At the prices they want

This summer I saw the
1st $200 car battery... crazy
1 Paper

Guy, as you ask,
How do batteri'es die?
You allso could have asked,
How do I keep them alive as long as possible?
I will try my very best English, please have patience :-)
My experience:
First, don't buy the cheapest, buy a decent quality, you will be rewarded. Litterally spoken you should carry a scale with you when buying a battery, because the heavier, the more lead in the bars inside. Buy cheap and you will have less lead inside = shorter life.
Over time, in the old type of batteries with lead bar's in acid, the lead particles will wander. Over time particles will wander away from the bars and they get thinner and particles settle on the bottom and build up and eventually will short the lead bars and the battry get's weaker and weaker and "dies". That's in short the battry life circle.
The harder you use it or charge it the more particles will wander and promotes the "death".
Power charge is life shortening to the battery, a good charging current is 10% of the capacity. On a eg. 40A/h battery that will be 4 Amps.
Another way to promote the death of a lead battry is leaving it partly or even worse fully discharged. Allways have the battery fully charged when leaving it. (this is not the case with NI CAD batteries, thats another story)
You should allways be able to measure 12,75v on the lead battery after several days / weeks. If the battery voltage drops slowly over a period, you have a bad battery. Off course after months the voltage could have dropped a little. But don't let that happen, a lead battery has to be maintained with some charging now and then when not in use.
I would say a normal good battry can last 5 - 8 years if you are gentle with it. It is the starter current that promotes the expiry date of the battery, so limit the usage of it to start the engine, and allways leave it fully charged.
The newer generations of betteries, gel batteries has got far more juice and are not that addicted to maintennance. When I had motorcycles I learned that I actually could leave the enclosed gel batteries, fully charged off course, for three - four months in the winther break without any attentions, fitted them in the spring and fired the bikes up with those batteries full of power.

Jan Kruber

As Jan points out I wonder if higher charging rates has something to do with it as years ago they seemed to die slowly and you could sometimes keep them going for a bit, but modern ones seem to just suddenly fail (ok yesterday but dead as a dodo this morning). I may be wrong but wonder if that is anything to do with dynamo versus alternator. I must admit Guy you have got me curious now as its not something I've thought about before.

T Mason

Sometimes peacefully, sometimes suddenly. ;-)
Happy New Year!
Bill Bretherton

Thanks Jan. A good description. I do rather like the idea of wandering particles of lead. It sounds like a rather nice existence ! I also quite like just wandering around.
But I do understand your meaning. ;-)

The background to this question is that I have 2 identical 60Ah batteries from 2 other cars. ( a VW and a SEAT) Both have been replaced so these are now just taking up space in the garage and I was wondering if there was any way of reviving them. They have those little tell-tale windows that change colour when the battery is charged.

After several days on the battery charger both tell-tales will go green. In this state (after leaving to settle down for 3 hours after disconnecting the charger) one battery shows only 9.7v so I assume that although some cells will charge up, there is at least one completely failed cell. The charger continues to show 2A current throughout.

Same process on the other battery and the charger drops to 0.3A and meter shows 12.6v, but still won't restart the VW which I find puzzling.

You might find this a useful read.

I've used the Adverc controller and a previous version (TWC) on sailing boats which by very nature put a high demand on service battery's especially night sailing etc.
The key thing to maintaining the battery was not to go below 50% capacity and the higher charging voltage to prevent sulphation.
Normal regulators keep the voltage low to prevent damage as they are pretty basic, it can be safely raised if controlled.

Not a sales pitch it worked for me and my batterys lasted about 8+ years, also the newer AGM's (absorbed glass mat) have addition benefits.
richard b

Also this

If you scroll down the menu on the side there are various usefull bits.
richard b

This probably makes sense about the reason for failure for these two batteries. Both cars are "moderns" with relatively sophisticated electrical systems - at least compared to our Spridgetty things! That artical does highlight the increased battery sensitivity of ""Executive cars with engine management-systems, telephone and on-board computers;"" and although not exactly executive versions the on-board requirements of even everyday models is now up with the expectations of executive variants from only a few years ago.

Low charged batteries make the pre-start on board diagnostic process go crazy with impressive New Year celebration standard light shows on the dashboard binnacle!

Both of these batteries failed after their respective cars had stood for several weeks so the charge levels had fallen really low by then. It was only after that the problems of getting them charged back up again began, although they could well have been on the way out anyway. From that second link this fits their description of Sulphation pretty well exactly!

Incidentally, I nearly had a Darwinian moment with one of these batteries yesterday!

Guy, I think that has a lot to do with it on moderns. One of the biggest drains on them seems to be the alarm and imobiliser systems especially if it is a sophisticated one. I know of a nineties car that will flatten a new battery in three weeks if it is not charged or used.

T Mason

I'm now a bit nervous of long/higher charging times with pretty dead batteries - I had one I tried to bring back to life while rebuilding the car to use for testing etc.

Left it on the workshop bench charging over night having checked/filled the fluid - following day found it was spewing acid all over the workbench !!
So killed the power to the workshop and left it alone until it had stopped gassing - likely acid in the air etc.

Lesson learned if it does not take a charge its probably knackered internally and no charging will bring it back.

Oh - another trick with the Adverc type charger - it has a temperature sensor that is placed against the main battery bank to avoid overheating during the charge cycle - would have helped in this situation.
richard b


Plenty of stuff on the web regarding "re-conditioning" of batteries with epsom salt solution....Hmmmm....

Try one and let us know!


My near Darwinian moment:
I had left the battery charging on the bench for a couple of days. I went into the garage, switched on the light and glanced at the battery tell-tale window, seeing it was green. At the same moment I realised that I had forgotten to remove the little vent bungs, and without thinking pulled one out. It hissed out gas for a full 6 or 8 seconds before my distracted brain cell slowly caught up with what was going on!

Another good reason for not smoking!

the application of Bat Aid or similar might help.

As I was told on here, the tell-tales only relate to one cell not the other five. I also found the system to be unreliable on the last battery that had it it showed black when the battery was fine.

For recharging some modern domestic battery chargers just won't charge a battery if it's too low for them. With my neigbours' batteries that are flat over the years I use a combination of a very old and basic 4-amp charger that I've had for decades then as a top up and check, as the old charger's dial is a bit difficult to interpret at the very bottom end, I used my 20 year old battery conditioner. The combination has only failed once. The thing is not to rush, it takes as long as it takes. I've never been able to try it but I'd imagine the battery conditioner alone, given enough time (up to 40-60 hours) would fully charge most flat batteries.

The battery conditioner was bought to keep the charge on a battery that was difficult to get at on a car that had an immobilizer and alarm that would reduce a full battery in two weeks so the car wouldn't start. I made a permanent connection for the conditioner directly to the battery.

My neighbour bought from Aldi a 15 (half price) combined battery charger/conditioner it's great we used it only yesterday.
Nigel Atkins

I can have no patience with these fancy, and useless, modern chargers which try to be too "smart" for their own good! Mine is a simple 50 year old charger that works perfectly, doing no more and no less than it was designed to do.

I might get and try some of those BatAid tablets though. Its getting close to my original question. Proper understanding of the actual mechanism of failure might provide a possible route to repair. Implication of that MGOC explanation is that there is potentially a simple chemical solution to at least the Sulphate build up problem.


When now Guy we need to define failure and dead - no we don't.

Some modern chargers are good that 15 Aldi one seems well worth its while so far, at least 3 years old I think.

I'd definitely recommend a battery conditioner, not needed for a Spridget without some electrical extras but it might be good for a modern car car that eats its battery whilst static for a while. You'd have to check though as those German cars have some very tricky programming. ;)

Now I was going to originally put up some like the MGOC BatAid bit but thought you'd prefer the wider exploration of the links I put up.

I'm sure I've put up BatAid previously to have it shot down - the price, if it works, you can make your own - I've never used it but would try if I had to. The battery(ies) is one of the first things I'd sort, after safety items, on an old car particularly the overpriced ones called classics as often they're not used enough.

I lost a very good link that gave a good explanation of what you wanted, as John Twist has said batteries are (probably) the most oversold car part (I can't remember to quote exactly).
Nigel Atkins

I've got a smart charger... and it says it can bring back batteries from sulifieds... I'm 50/50, some times it does and sometimes it won't

The bad thing about the modern smart bat, is they won't charge once the bat voltage drops below 9 volts??? So you have to trick them with a charged battery added to the old battery

Guy... give a auto salvage yard a try... I'm very happy with my $15 one I got the other day... even if it goes bad in 6 months... I'd get every dime out of it... it's not the perfect size (to small) bugs done perfect with this cold weather of around zero the past 2 weeks

It's really tough to justify the price of a new battery (the replaced the lead with gold I think)
$200 vs $15 is a huge difference in price... and mine came with 15 day exchange slip in case it was bad when I got home

I drop $15 for 2 trips to McDonald's

1 Paper

I'm not in the market to buy a replacement, Prop, just experimenting with these old ones before they get chucked out!

But I have bought scrapyard ones before and agree with you that they can be very good value. For some reason on an ailing car, people often seem to end up buying a new battery shortly before the final journey to the breaker's yard and so for 10 (what the local place charges me) you can get an almost brand new one!

Some manufacturers these days use smart batteries which need to be programmed to the car or they may not work. A bit of information here
David Billington

Best thing for a little used vehicle is a battery isolator switch. My midget has one with a removable (big red) key. I've just bought two of the old Lucas type for my campervan (because it has a deep-cycle domestic battery as well as the engine cranking battery).
Because the van has a mains cable connection I'm also planning to have two permanently fitted battery conditioners. They needn't cost a lot.
The usual culprits for pulling batteries down in lightly used vehicles are retrofitted stereos and the starter motor. Not so much inertial starters like most Spridgets have, but older pre-engaged starters are buggers for leaking juice and flattening batteries.


I agree with your path if your trying to recondition them ... fresh acid, and put a smart charger to de solidify them and see what happens ... even if you get another year out of em that's a good reason to try it

Just keep some jumper cables close by

1 Paper

Getting sulphuric acid these days can be tricky so I've been told by a chemist I know as it is one of the main ones used in acid attacks and is also used in the production of illegal drugs and so access is much more tightly controlled than it used to be. I have some for pickling silver soldered parts from back in the day when you could walk into the chemical supply house and buy what you wanted, I'm not aware of it having a shelf life and it's in a glass bottle. I have hydrochloric acid which is readily available on ebay and last I bought earlier in the year was specifically bought in a glass bottle as my previous experience with it in a plastic bottle is the HCl slowly leached out and rusted anything steel in the local area.
David Billington

Why would one need to top up the sulphuric acid? Surely any evaporation will be of water, leading to increased concentration of the acid. That's why the recommendation was to only ever top up a battery with distilled water, at least back in the days before sealed batteries became the norm.

My thought was to replace the acid, with new as I'd think acid gets both polluted and tired over time
1 Paper

I think that that bringing dead batteries to life again is rather theoretical.
Most likely the batteri has a cell broken down or it has a large amount of lead particles in the bottom build up over some years, shorting the batteri.
If it has a broken cell the battri is't definitively game over.
If the battry suffers from lead build up in the bottom, lets say you could empty it thoroughly, so that no lead particles are left anymore, it might be possible to wake the battery up again with new acid of the right electrolytic grade - providing the bars still have enough lead ..... theory...
Jan Kruber

Madeline Usher would have you check that the battery is actually dead before you bury it!
Nigel Atkins

old trick used to be a teaspoon of baking soda in each cell, then fill each cell up to the top with water and give it a big charge up on High---this purges the rubbish out of the battery--It's messy and the battery needs to be somewhere so the overflow doesn't cause a problem but it has a fairly good success rate
William Revit

You wouldn't want the charge to go on too long on a high charge.

Big high charges from big high quick chargers can often kill rather than cure, sh*t or bust approach sometimes.

Slow discharge wants slow recharge.
Nigel Atkins

This thread was discussed between 29/12/2017 and 04/01/2018

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