The only way I can monitor the charging current from the alternator is by using VCDS, after starting, it charges at a fairly good lick, can't quite remember now, but ~ 16/20A?, but only for a few minutes...... even if the battery is well below its 85% SOC, it then just trickle charges at around, again I think, 1 to 2A or so at a terminal voltage of 13.5/13.6V, I presume this is in the interest of fuel savings since the BMS can and does use variable voltage charging right up to almost 15V which would certainly force more amps into the battery to get its SOC up relatively quickly. Modern Alternators give fantastic output though, even at idling revs, at idling, with headlights on full beam, HRS on, and fan speed on 3 (normally 2) the alternator will still charge the battery, in effect, this means, that the battery will never discharge while the engine is running, even if only idling.

@Johngerard You put 85% state of charge, I've seen various figure for the VW SOC to allow for regenerative lip-service, does the VW programing change SOC to allow for registered used/charging, allowing for use, abuse, neglect of the battery plus no doubt a good margin for tardiness of battery replacement and/or a possible potential healthy spare part revenue and profit in house?

And/or has the programing changed over the years and/or models and years?

HRS had me thinking, almost looked it up then a rare brainwave - heated rear windscreen.

I don't think you would be challenging the alternator as much as some drivers at idle especially those with fully-loaded toys on/in the cars, then electric load when the car is stopped or parked up with engine off, and also perhaps a spider's nest of wire connectors for this, that and gawd knows what.

Of course battery and alternator work as a pair and though as you say these alternators are good having reasonably heathy battery(ies) partnered up to them helps with the alternators longevity and of course a reasonably healthy alternator will help with battery(ies) longevity.

I have sympathy with the car manufacturers as modern drivers generally aren't interested in knowing much about the basic running of the vehicles and any information offered on the dash can be misunderstood as the explanations won't be read even if offered in the Driver's Handbook (to go old school) and many would sooner just replace the battery than care which is fair enough but a waste of materials (time money and hassle to me) and of course it helps a little with the national economy (of several countries).

Funnily enough this Saturday I'm going to check on a Jag's double battery (stop/start) set up, no more than multimeter probes on the batteries terminals to see what the readings are after last week's sort out, and check no error codes have returned with vehicle use. Only very basic stuff, if recharging the battery last week with an appropriate battery charger maintainer has sorted all of the warnings and (almost) all of the error codes, great if not, well it's a modern Jag (Land Rover, TATA) then it's off to very expensive battery supplier and/or Jag sorter-outer. The Ford Jags seem to tell on non- Jag scanners being used the TATA Jag might do but it didn't show it, possibly grateful for all the help they can get. 😄

Edited 19 March19 Mar by nta16
ETA: tag

Update: Heres a thing, battery charger shows its charging the battery 'CTEK' "recond mode" now showing light No.6.

Its been hooked up two days now. I went to unlock the car today and the indicator lights on the wing mirrors flashed - not the indicators - but the wing mirrors didn't unfold. I check the charger - results as above - and then pressed the remote to lock the car. Once again the wing mirror lights flashed but nothing else. The car doesn't lock. So is there a fault with the battery or an electrical fault elsewhere? I tried the boot opening button with the remote, it clicked and unlocked but didn't open. Which uggests to me that there is no power in the electrics. I'm happy to go buy a new battery but don't want to waste money if thats not tyhe problem. What would be the next step?? Getting the electrics/battery/system checked? I'm not happy with the Skoda garage I took it to last week fro a service and MOT so would a decent local garage be able to sort this kind of issue? Really not sure why it's all gone to rat sh!t this week .

46 minutes ago, DaddyDan said:

Update: Heres a thing, battery charger shows its charging the battery 'CTEK' "recond mode" now showing light No.6.

Its been hooked up two days now. I went to unlock the car today and the indicator lights on the wing mirrors flashed - not the indicators - but the wing mirrors didn't unfold. I check the charger - results as above - and then pressed the remote to lock the car. Once again the wing mirror lights flashed but nothing else. The car doesn't lock. So is there a fault with the battery or an electrical fault elsewhere? I tried the boot opening button with the remote, it clicked and unlocked but didn't open. Which uggests to me that there is no power in the electrics. I'm happy to go buy a new battery but don't want to waste money if thats not tyhe problem. What would be the next step?? Getting the electrics/battery/system checked? I'm not happy with the Skoda garage I took it to last week fro a service and MOT so would a decent local garage be able to sort this kind of issue? Really not sure why it's all gone to rat sh!t this week .

AI says:

Detailed Meaning of Light No. 6 (Recond Mode)

• Active Reconditioning: The charger is adding a special step (Step 6) to the normal 8-step charging process.

• What it does: It applies a higher voltage—around 15.8V—to create controlled gassing in the battery, which breaks up acid stratification.

• Duration: Recond mode adds between 30 minutes to 4 hours of extra charging time on top of the normal charge cycle.

• Indication: When this light is on, the charger is actively working to restore the battery's capacity, not just charging it.

  CTEK +3

Key Considerations

• Battery Type: Only use this mode on Flooded/Wet or Calcium/Ca batteries.

• Warning: Do not use Recond mode on AGM, GEL, or Lithium batteries, as the high voltage can damage them.

Ah, very useful, Thank you. I appreciate the info. I'll let the kit do its thing then - and leave it alone.. cheers.

I agree that I've always seen high charging when on the over run, this year only, is the first time that I've spotted that the charging voltage is always high when the ambient temperature is very low, it must have been happening in the past 5 or so years that I've been "glued" to the plug-in 12V DVM.

Maybe what was concerning me was that I changed the still useful 59Ahr EFB for a 70Ahr AGM in my wife's 2015 VW Polo - just because it was then over 10 years old and on its original Exide VW Group battery - and the charging "behaviour" was not exactly what I had expected for a new battery, especially in winter. Now that the temperature has risen, that is no longer an issue heading into Summer.

Edited 19 March19 Mar by rum4mo

2 hours ago, DaddyDan said:

Ah, very useful, Thank you. I appreciate the info. I'll let the kit do its thing then - and leave it alone.. cheers.

Why not look at the instructions for whatever CTEK model you have or download the PDF copy if you don't have the paper copy.

Do say you did follow the instructions in the car's Owner's Manual for hooking up the battery charger maintainer.

As I have a PDF copy of the CTEK MX 5.0 I can copy and paste those here. -

"Recond option 15.8V/1.5A

Use to return energy to the empty WET and Ca/Ca batteries. Recond your battery once per year and after deep discharge to maximise lifetime and capacity. The Recond program adds STEP 6 to the normal battery program."

This confirms the "AI" (artificial yes, intelligence no it's not) - always confirm and cross reference any information you get from any source but especially "AI".

The CTEKs, like many others, are called "smart" chargers, like other devices called "smart" devices, they are not they actually very dumb and sometimes need fooling to do what "dumb / ordinary" charges would just get get on and do.

The CTEK MX 5.0 instructions have step 6 Recon with a "time limit" of "2h or 6h" which add confusion as it shows a AGM Recond setting (of 1.5.8v same as other Recond) so if your CTEK doesn't go to stage/light 7 after say 2, 4 or 6 hours then it might not have been able to complete it's task.

Lidl are selling the £15 charger maintainer for £10 from IIRC next week I'd sooner have one of those than a CTEK personally having seen the three CTEKs my mate has, he could have saved a lot of money.

I don't like the sound of your unlocking and locking issues at this stage of charging but I don't know how the CTEKs bugger about, but stage 6 ons the instruction for the CTEK MX 5.0 suggest to me that stages 1 to 5 take a maximum of 36h 3 min or 44h 3 min depending on how you interpret the markings - and it also depends on what you mean by two days, if less than those two figures perhaps the CTEK is doing fine and just needs to complete its work.

I don't like to see batteries changed unnecessarily and prematurely but sometimes and for some that is the best option and then I suggest before installing fully charging the new battery to 100% that way you have a very good datum point for reference (should there be other or further charging or other issues with the car) and you know the battery was fully charged when fitted. Yes the VW programing will get it down to about 80% but that won't be too much of a factor on very early checks of the new battery to confirm against and charging or drain issue(s).

Let us know how things are going.

Hi, Thanks again.

Yep, all hooked up as described and illustarted in the manual - Positive on the battery and negative on the cars 'earth point' which I scrubbed-up clean beforehand. As you say the CTEK might just be doing its thing. It's coming up to 30 something hours since attaching it. I don't think the battery would have had any charge other than when it's running so maybe it needs it or it's to 'tired' to go on !

I'll wait to see if the display ligths change anytime soon.

I've borrowed this charger but will be getting a 'normal one' for future battery health as described 👍🏻

One thing or issue I came across with any CTEK smart charger is, the instruction manual claims that once you have set the "mode" the first time, and if you are then, some time later using it for the same, then it will have remembered the previous setting.

I found out, much to my disappointment, that it can not always be trusted to operate like that.

What happened to me was, I had left my own car connected up for a couple of days or more, as I had used it previously many times, I just connected it up and switched it on - waited to see that it was indeed charging as expected, ie the LEDs were lighting up sequentially, and left it to get on with things. A couple or so days later, all looked good, ie it was at the end of the prog'd range of LEDs - but for some reason, I measured the voltage and it was presently at the CTEK "safe low level" - luckily I had not planned to need to charge up another battery just then as my car's battery had essentially been discharged instead of charged, so I cycled through the charging mode options, and that sorted that out. Now I always cycle round all the charge options before walking away, and so far no more charging problems.

Cheers, good bit of advice and worth remembering. Thanks.👍🏻

Sooo…….

The short story is;

no matter what the CTEK showed indicator light 4 or 5 - it stuck there whichever ‘mode’ it was in. I cycled through the modes and tried normal car charge. After 24 hrs no change. Measured the voltage across the battery and all it could muster was 9 volts. So I’ve declared it ‘dead’ !!

My question now - and just to confirm - if I buy a like-for-like EFB battery will I need to code the car (or whatever it is I have to do with an AGM Battery) ???

I would definitely get it coded, may cost you nothing if you buy in the right shop.

Re battery charging, Lidl sell a Ultimate Speed ULGD 5A charger with a inbuilt voltmeter, very useful, for around £15, only drawback is that it will not charge a "flattened" battery, if voltage < than something like 8/9 I think.

Also check that your Alternator is OK.

Edited 22 March22 Mar by Johngerard

As previously put it's a probably best that you have the battery 'coded' but other owners have said that when swapping from an EFB to another EFB with the same Ah rating that they were happy with the results a year or too later. Certainly I know the world will not end even if you change from EFB to AGM and at a slightly different Ah and don't get it 'coded' absolutely immediately, I have lived to tell the tale.

I'd not trust the CTEK not to possibly kill or not be able to deal with a battery in a very low state of charge and health but as with the £9.99 Lidl charger maintainer it can possibly be 'outsmarted' to charge a battery below 7.5V(? IIRC). I've recharged a battery from 2.5v and not because I'm that smart or clever just better at it than a "smart" charger, not that I would trust that battery for much or long, certainly not on a very modern car.

Edited 22 March22 Mar by nta16

On 22/03/2026 at 18:06, DaddyDan said:

Sooo…….

The short story is;

no matter what the CTEK showed indicator light 4 or 5 - it stuck there whichever ‘mode’ it was in. I cycled through the modes and tried normal car charge. After 24 hrs no change. Measured the voltage across the battery and all it could muster was 9 volts. So I’ve declared it ‘dead’ !!

My question now - and just to confirm - if I buy a like-for-like EFB battery will I need to code the car (or whatever it is I have to do with an AGM Battery) ???

Just for interest I used a Ultimate Speed ULGD 5A charger on my battery for over 8 hrs. Before charge the Battery at rest Voltage was 12.5V, Battery Charge level (SOC) 76% and Usable Battery charge 24AH. Afer 3 hrs, where the charger ouput was 4.0A at 13.4V for ~ 8 minutes, then ~ 5 minutes at 1.1A, it then reached 14.4V and cut out until voltage fell to ~ 13.1V, then commenced recharging at 1.1A for another few minutes and then stayed trickle charging at 0.25A at 13.4V for those almost 3 hours, battery readings then, at rest voltage 12.5V, SOC 76%, Usable Battery Charge 25AH (increase of 1AH), left on charge for another 5 hrs with no change in above readings, just trickle charged at 0.25A at 13.4V. The ULGD allegedy trickle charges at 0.1A at 14.4V but mine certainly didn't, as soon as it hits 14.4V it shuts down until the voltage falls to 13.1V. One way or the other don't think this does anything for this battery in its present state of 76% SOC. The Alternator does get it up to 80/85% eventually, but I did notice that its lowest charging rate is ~ 1.0A at 13.5/13.6V.

Edited 26 March26 Mar by Johngerard

Too late at night for me to look at figures in text but the Ultimate Speed ULGB 5A sounds very disappointing, perhaps they're not as well made as they used to be or different a manufacturer(s) were used previously or now. I've previously put up illustrations on Briskoda from this charger, I'll find them and post here later.

Edited 27 March27 Mar by nta16

Here they are. -

Thats the one, Nigel.

Should also maybe have mentioned that some time ago, I put this charger on a 11 year old 44AH Varta lead acid battery installed in another (22 year old) family Polo and the charger worked exactly the same, this battery of course would have been Alternator constantly charged at 14.4V throughout its long lasting life.

As the unit has changed over the years but kept the same name out of interest what IAN number does yours have?

Yesterday I had to repair the charging leads on my neighbour's 12 year old Aldi charger (Auto XS CPL 2054) as the leads had been wrapped and stored badly, tested it on my wife's car for 15 minutes or so and it seem to register its progress, that cost £15 at the time (I didn't realise it was quite as long ago as as 12 years but time passes quicker as you get older). As I've put before he has successfully used that many times over the years as their 1992 Merc sees very little use for a number of years now.

On my wife's 2015 Fabia with AGM battery, and other cars, I use, and recommend, a Ring "smart" (they are not of course) 4-amp charger maintainer now superseded by the Ring RSC904 which has always done very well. I also use a 30+ year old 4-amp "dumb" inexpensive charger and 20+ year old "smart" of the time 1.8-amp, middle expense, charger maintainer. Even with those three and lots of time and patience and some experience some people can get their batteries beyond much reasonable further use, other than out of the car.

IAN: 383685_2100S./N:278007

It also has Manufactured: 2022/35 above the IAN details.

It's a ULGD 5.0 C1

Nearest I could get from Lidl UK was IAN 383685_2110, model ULGD 5.0 C1 - 2486, year 2022/35.

https://media.sit-connect.com/public/articlemanual/ae9b8786-ac8b-45d8-93d3-d7b8339be425.pdf

This guy didn’t have much luck with his Varta EFB’s. Gone through 2 of them in 4 years. First one just over 2 years and the second 18 months. High mileage driver and mostly disables start stop.

I’m not fully happy with the Varta in my 2 year old vRS. I think it should be better for it’s age. I often get low voltage codes. The odd time a morning crank sometimes sounds a bit low. The car doesn’t do short runs. It has 60k in 2 years.

Just to add, i did a lot of miles yesterday so this morning plugged in the obd. Battery state of charge only 66%.

Edited 9 May9 May by Micky 32

Try using an appropriate battery charger following the instruction in the manuals and fully recharging the battery to 100% slowly (2, 3, 4, 5=amps charger) rather than letting car's computer dictate only 80% charge. If it's not too late this should help improve things.

The higher mileage depends on the type of driving and electrical use during the driving and when arked up. Even at 30k-miles a year the car is only driven a fraction of the time to it not being driven. What's running on the car, other than all the computer systems when it's parked up.

Try the (preventative) slow charging to 100% (could take many hours) and see how that might improve things (if not too late).

I would always consider a VW prgaraming issue over any Varta battery possible faults (11 times out of 10).

Most of us on here are enthusiasts and we love nothing more than popping our bonnets up and putting chargers on our batteries etc. i do have a neat little smart charger but it doesn’t have a EFB setting just normal or AGM. I’m guessing that can’t be used?

However there’s a 70 year old lady up the road from me who owns a 2024 Octavia. I can’t imagine her ever putting a charger on her car or caring about chargers.

Interestingly i know 2 ederly people. One has a 3 year old VW Tiguan and the other has a 3 year old Opel(Vauxhall). Both have start stop and EFB batteries. The VW has a Moll battery . His battery reads healthier than mine on the tester despite his being a year older and doing shorter journeys .Both drivers only do about 5k a year and never have any battery problems. The Opel owner was recently in hospital for 6 weeks and his car fired up instantly.

I’d say higher mileage and use have a big impact on those batteries. Constantly cycling from brake regeneration, more starter use, subjected to more heat. If i connect the obd11 to my car at the end of the day the temperature of my battery can be as high as 40 degrees+.

My vRS puts the battery through more use than my old 2017 Passat. I’m guessing stricter emissions laws are forcing car makers to make more use of the battery. My current total throughput energy and charging throughput after 2 years is over 11000ah. My old Passat after 2 years with similiar mileage and use was 8500ah.

As for the electrics when i’m driving all that would be on is the AC on auto , infotainment system and the LED lights on auto. I never use the heated seats etc. The odd time i might use the heated steering wheel if it’s very cold but that would only be on for a few minutes.

6 hours ago, Micky 32 said:

i do have a neat little smart charger but it doesn’t have a EFB setting just normal or AGM. I’m guessing that can’t be used?

If it has an AGM setting then I'd be surprised if it can't do a EFB battery which is just an enhanced normal battery (Enhanced Flooed Battery), you're old emough to know the old saying if all else fails read the (charger) manual.

I've lived amoung old people for 44 years whether they can afford a 2024 Octavia or not they pay out for the most exopensive ways of getting the battery changed for their convenience, usually leaving thingsuntil it's a distress (premature) purchase.

Same as with house electrics different drivers use different amounts of electric even in the same house and cars so difficult to do comparisions. VW's programming seems to be harder on batteries and they put in the cheaper type of battery from factory, even on their own Father car brand. Proportionately potentially at least higher mileage cars will have less starts and brake regeneration, unless in congested traffic often. It's the AGM batteries that are supposed to be more delicate to heat.

Auto air-con is a big electric consumer and the newer the car the more interfering and informing "aids" and "assisits" to be powered. I fyou use thing like see-me-home (or whatever they call having the headlight on as you leave the car). Then only the other day I read about something to do with the park lights on IIRC even on my wife's more limited "aids" and "assists") 2015 Fabia it can be very draining on the battery and you might not realise you put this setting on that doesn't turn off under quite ordinary condition (sounded like another VW programing balls-up to me, but it's in the 'Owner's Manual'.

The VW programming of keeping the battery charge to only up to about 80% isn't good for battery longity which is why I keep suggesting charging it to 100%, giving it a birthday and Xmas, or charge it badly needs. But I can understand if someone doesn't want to bother with wasting more life time and force farting about with cars. I just wanted prevention from VW battery programing upsetting my wife by making the car have another hassle.

Using 11,000 Ah (if the computer programs have this correct) doesn't matter if around closer to 11,000 Ah is put back in, the battery will still age and deteriate but at least at a slower rate and the alternator also gets a little bit of relief now and then.