11.8 volts but just 110 CCA

[belfry]

I wonder if I can pick your brains please?

My Mum has a 2001 MB 320SLK. For the past year she's been having problems with the car not starting some mornings and the battery seems to be unable to crank the car over. After a charge/jump it works for a few days then the problem recurs.

Her garage have been replacing the battery and charging for a new battery. In June this year I put on a 640 CCA 60Ah Halfords battery. It was flat this morning having been fine since June. I took the battery back to Halfords for a refund and the checked the battery health. 11.8v and 110CCA.

The spec for the SLK320 is 780CCA and 77Ah, so I wonder if the alternator might be destroying the cells in these batteries?

I have run numerous parasitic drain tests using the method of connecting a multimeter between the removed earth terminal and the earth cable, but I have not been able to find any unusual parasitic drain (this would have been something to work with).

Any thoughts please?

[GreenV8S]

It's possible there is a charging system fault or excessive parasitic drain. Parasitic drains in particular may not be obvious during a spot check. I suspect the problem is more likely to be a combination of normal parasitic drain and insufficient use for the battery to fully recover after each use. In that case it might pay you to wire up a battery maintainer to keep the battery charged between use.

[belfry]

Thanks for the reply. I have spent many hours over the last year checking (at various times of day and night) for a change in the amps. In all of this time I have struggled to find anything above about 0.03, normally nearer 0.01. My mum only uses the car for short journeys which might not help the battery. What about the idea that the alternator was too standard powerful for the under specced battery?

[Caddyshack]

Have you had the alternator efficiency checked?
My mil only does 1-10 miles ever and not frequently so the alternator does not have a chance, your mums car probably has far more advanced electronics so expect the alternator is not having chance to charge the battery and it is draining whilst driving.

I fitted a little gadget that senses voltage drop and immobilises the battery if not running, you have a key fob to press when you get out and it disconnects the battery but will cut off if you forget when the battery drops, before you get in and unlock you press the fob to reconnect the battery. Her car has been good since but still needs a good charge Every 2-3 months as she does not drive far enough Ever to charge the battery.....I found the gadget on here via the tvr forum but can’t remember the make.

Also, the AA sell a solar panel that plugs in to the obd port and gently charges the battery by leaving it on the dash.

[Caddyshack]

Here you go, this is what I used https://www.batterybrain.co.uk/

[Penelope Stopit]

No, the alternator doesn't care about what size of battery is fitted

30 Milliamps seems very low

Are you sure the ammeter is accurate?

Alternator overcharging will damage batteries

[Sheepshanks]

How often is the battery being charged? Bear in mind alternators don’t do much more than float charge the battery, so they need hours of running, not a few mins now and again.

[belfry]

My mum drives 3 miles to the shops and back 2-3 times a week. She is 83 and not interested in longer trips to charge her battery.

I can see why the battery might not be charging fully, but why is there such a reduction in the oomph of the CCA at 110 vs a capacity of 660?

[paintman]

Maximum of 3 miles each way with at least two starts?
With that usage the alternator has no chance & I'm not surprised the battery voltage is that low & that she's had issues.
Be even worse if other electrics - lights, wipers etc are also in use.
You could consider having a check by an auto electrician & a diagnostic for any stored codes just to rule it out but I think it's the usage that's the problem.
You do need to have the alternator output checked.

Edited by paintman on Friday 25th September 11:41

[Smiljan]

I'd agree that the short infrequent trips are a good likely cause of your issue. It's worth checking for parasitic drain though, the car is quite old and there may be an issue with ground connections too. When you measure the parasitic drain put an amp clamp around the main battery wire near the battery and check when the car shuts off there isn't excessive current draw.

Most modern cars take a while to shut everything down completely so you may have to wait ten minutes or more to be sure. Somewhere less than 25mA would indicate there is no issue with parasitic drain.

There's a great article on the battery university site to explain what may be happening. If it is the short journeys and she doesn't want to change her habits you may have to just pop a battery charger/conditioner on it every couple or weeks for her to make sure it gets looked after (if that's practical for you).

https://batteryuniversity.com/learn/archive/what_c...

Lastly you could get her on of those solar chargers and have her leave it on the dash when she's not using the car. There are few on Amazon for around £20 or £30. All depends if the car sits in an non shady area when it's parked up or not.

[Sheepshanks]

belfry said:

My mum drives 3 miles to the shops and back 2-3 times a week. She is 83 and not interested in longer trips to charge her battery.

I can see why the battery might not be charging fully, but why is there such a reduction in the oomph of the CCA at 110 vs a capacity of 660?

I'm not really up on the technicalities, but batteries that were kept at low charge used to do a thing were they suffer from stratification - as I understand it, it's like only the bottom layer of the battery charges.

Wife had a used Fiesta years ago that came with a massive battery and it often wouldn't start. I stuck the battery in my company rep-mobile and it was absolutely fine, and the normal sized battery from that car was fine in the Fiesta.

I've got an older Merc (2005 model C270CDi) which I don't use much and that wouldn't start last winter on its original battery after I hadn't used the car for few weeks. There's a massive water cooled alternator on the car and AA man tested the battery and it was charging at 14A, which he said was normal. I think it's 100Ah so it's going to take several hours of running to fully charge the battery.

I think in your case you're just going to have to stick a charger on every couple of weeks. Or take the car for a good hour+ run. Or swap the car for a Honda Jazz.

[Caddyshack]

Sheepshanks said:

belfry said:

My mum drives 3 miles to the shops and back 2-3 times a week. She is 83 and not interested in longer trips to charge her battery.

I can see why the battery might not be charging fully, but why is there such a reduction in the oomph of the CCA at 110 vs a capacity of 660?

I'm not really up on the technicalities, but batteries that were kept at low charge used to do a thing were they suffer from stratification - as I understand it, it's like only the bottom layer of the battery charges.

Wife had a used Fiesta years ago that came with a massive battery and it often wouldn't start. I stuck the battery in my company rep-mobile and it was absolutely fine, and the normal sized battery from that car was fine in the Fiesta.

I've got an older Merc (2005 model C270CDi) which I don't use much and that wouldn't start last winter on its original battery after I hadn't used the car for few weeks. There's a massive water cooled alternator on the car and AA man tested the battery and it was charging at 14A, which he said was normal. I think it's 100Ah so it's going to take several hours of running to fully charge the battery.

I think in your case you're just going to have to stick a charger on every couple of weeks. Or take the car for a good hour+ run. Or swap the car for a Honda Jazz.

Yes batteries can do this,...Also we had a Volvo XC 90 early one and if the battery drained then the alternator would only ever charge back to where it started from, so you had to give it a good charge every now and again, the Volvo specialist checked it and said many of the early ones did that.

[Caddyshack]

belfry said:

My mum drives 3 miles to the shops and back 2-3 times a week. She is 83 and not interested in longer trips to charge her battery.

I can see why the battery might not be charging fully, but why is there such a reduction in the oomph of the CCA at 110 vs a capacity of 660?

Because the alternator has no chance of getting it back to optimal state of charge and I suspect the battery cells are being damaged.

Modern batteries do not do well sitting unused on the cold, they need regular up and down work.

You Mum needs a trickle charger or one of the OBD port solar chargers (doubt this will be enough on its own) and one of the battery isolators that I posted.

[belfry]

I can guarantee that if I attach a CTEK trickle charger to her car, she will complain about a rattling noise as she drives along (which will be the trickle charger dragging along the road as she heads to the shops)

[paintman]

belfry said:

I can guarantee that if I attach a CTEK trickle charger to her car, she will complain about a rattling noise as she drives along (which will be the trickle charger dragging along the road as she heads to the shops)

I LOL'd at that

[Smiljan]

belfry said:

I can guarantee that if I attach a CTEK trickle charger to her car, she will complain about a rattling noise as she drives along (which will be the trickle charger dragging along the road as she heads to the shops)

[GreenV8S]

belfry said:

why is there such a reduction in the oomph of the CCA at 110 vs a capacity of 660?

Because the battery is completely flat.

[Penelope Stopit]

belfry said:

I can guarantee that if I attach a CTEK trickle charger to her car, she will complain about a rattling noise as she drives along (which will be the trickle charger dragging along the road as she heads to the shops)

Buy her one of these




https://www.ebay.co.uk/itm/372591930620

[Caddyshack]

Penelope Stopit said:

belfry said:

I can guarantee that if I attach a CTEK trickle charger to her car, she will complain about a rattling noise as she drives along (which will be the trickle charger dragging along the road as she heads to the shops)

Buy her one of these




https://www.ebay.co.uk/itm/372591930620

Yes, Ctek has a break / fly off lead just for that reason.

This is also why I said to use the battery immobiliser that I recommended and the obd port solar charger.

I experienced this exact same thing with a very dopey and forgetful 80 yr old mother in law who gets everything wrong and the above is the solution after many failed attempts.

[belfry]

Caddyshack’s suggestion of installing a device called a “Battery Brain “ is a good idea. I have now fitted one. It connects to the battery and cuts all power if the battery level drops to anything less than 11.5v. This will mean that a parasitic drain is impossible with the battery disconnected. There is a reset switch to restore power.

The alternator failed last week so I have replace that with a new one. I’m sure that the regular chore of charging a very flat battery has killed the alternator. But, could a faulty alternator have caused the original occasional parasitic drain?