Can anyone offer an explanation as to what is going on?

The fact that it appears to be totally fine in between spak attacks is the bit that has me stumped. Surely if it had a buggered cell it would always be playing up?

Sorry but batteries do have intermittent faults.

If you are reading very low volts at the battery terminals and the inbuilt hydrometer is working and reads charged....no question you have a problem in the battery.

Your logic is influenced by your dislike of the need to purchase a new battery.

cheers

BTW..how old is this battery.

The design life span of normal lead acid batteries is about 2 years.....if ya lucky you may get 5 years out of a battery....but by that time it may still be cranking the engine but it will be way below spec.

if the battery is more than 2 years old and giving problems.......just replace it.

cheers

No Bantam - my logic is influenced but my lack of understanding as to how batteries work. I would have thought that a buggered battery would be buggered all the time, not on an intermittent basis.

Happy to buy a new one if that is what will solve the problem.

I will be taking it for a load test to confirm that a new one is required (which, based on the responses so far, seems most likely).

I'd have to check but I think it is over 2 yrs old.

Don't rely on the load test...it may load test perfectly fine...well within the expectations of a battery of its age.

Only if the particular fault is occuring at the time will it test badly.

Remember when the fault is not occuring it cranks the vehicle.

Everything and I do mean everything can develop intermittent faults.

All to often I find that people insist that it cant be that or it must be this....because it worked....whenever.

If something was working at the time....that is not what matters....what matters is what was occuring when the item did not work.

If the measurements and observations where correct.....a battery failing to start the vehicle, hydrometer showing green and a measurment of 4 volts across the battery terminals.
AND a previous histrory of the same problem.

There is a problem with the battery.

Just about any 12 volt battery measuring 4 volts across the terminals is toast for one reason or another.

Nobody wants to believe that the in specificaton service life of a standard car battery is arround 3 years.

cheers

cheers

bantam... youve obviously nevervbeen on the overlander forum
I had a battery that no matter how much charge it was given would not start my vehicle.... replacing the battery fixed the issue.
I was told id wasted my money because apparently batteties like that can magically be repaired

yeh ..right.

cheers

I must be really lucky as the last 3 vehicle batteries have lasted 5 years, of The current vehicles one is 3years old and the other has had the red showing on the battery for the last 2 years since the vehicle was week old.

Guess I will have to be a believer and replace my batteries. Please send money so I can do that.

Yeh its not unusual for batteries to contunue cranking the engine well inti the fifth year...my best effort was 7 years....particularly in vehicles where the battery fitted has ample reserve capacity

But most batteries will be well below spec after 3 years if load tested.

cheers

engine type makes a difference too.
batterys in petrol vehicles usually last much longer due to less demand on them to turn the low compression engines over and they will keep starting a petrol long after there too dead to start a diesel

What can happen with a battery is a chunk can shed from one of the lead plates and largely short out the cell by shorting the plates.

In 90% of the cases, this is a total and irreversible battery failure.
However, you may have one of the rare instances where charging the battery moves the offending chunk and the battery "unshorts" itself.

Years ago, when all batteries had an unscrewable top on every cell, we would often give crook batteries the "Epsom Salts treatment."
This involved picking up and shaking the battery, then inverting it over a plastic tub and draining all the sulphuric acid.

We'd then fill the battery with warm water and shake it again and invert it to wash out all the accumulated crap.
Then we'd make up a mixture of Epsom Salts and warm water (stirred well) and pour this brew into the cells.

We'd leave the battery overnight and then shake, invert and drain again - then flush with clean water to remove all the Epsom Salts.

We'd leave the original acid to settle and decant the clear portion of the original acid back into the battery and then top up with fresh acid.
The battery would then go on the charger at low amperage for a couple of days to see if it would hold charge again.

About 30% of the batteries we treated would recover and be useable for another 6-12 mths on average - but overall, the efforts involved in trying to recover dead batteries were generally agreed on as not being worth it (batteries cost less back then, too), so we gave up on the stunt.

There's some good info in the link below.

Corrosion shedding and internal short

Thanks for those links - I'll check them out.
Not at home now and can't recall the battery brand.
Nothing new fitted recently.

Mine has a similar issue now, but happens over about 5 to 7 days of non vehicle use . . . still have to do that parasitic drain test on my rig.
After a week, mine just turns over, not enough to light up the glow plugs I feel.

If testing your battery voltage after a full charge, I think it's required to leave it for about 1/2 an hour for things to settle to get an accurate reading, which should be around 14v, then test it again after 24 hours and see what change there is (by the sounds it should be flat, which could be as low as around 10v or 11v reading ? Someone more knowledgeable might be able to confirm.)

That liottle window is most definitely a hydrometer...it is achanber that contains two balls of differing densities.....the red or green one shows depending on the SG of the acid......if the electrolite level is too low they simply don't work and the red ball may show.

The little window has everything to do with the charge in that cell.

a battery reading such low voltas at the terminals at any time is buggered.

cheers

Yes I agree on a few things, how old is the battery? Are there any electrical devices connected to it that could be drawing down current? If the battery is around 3-4 years old there is a good chance it needs replacing, usually notice this during winter. After all this you can get it tested by any auto elec or battery house to confirm.

Thanks Allan - that's a good idea. I used the multimeter as it was a quick way to check.

However, as Bantam said above, do not rely entirely on a load test, it may test OK but still have a problem such as self-discharge due to disintegrating plate sludge. And it could be an intermittent fault.
However, it is an easy test and may reveal a faulty battery.

If it comes thumbs-up then you move to the next investigation such as a load discharge. But even that could be intermittent and not show at the time you investigate.

Electrical fault finding requires logical progressive testing although an experienced technician may look to likely possibilities first.

I have a brake controller but not Tekonsha.

A Voyager by either Tekonsha or Hayman Reece would do that

G'day Wayne
Haven't noticed any pattern.
Does have a fob for access although it doesn't work properly - I have to use the key.
I guess a load test is the next step.

Thanks for bringing us up to date Krooz.
Let's hope it is the end of your problems.