had my battery checked?

[paddywack1878]

Is my battery slowly dying, i had it checked at my local battery specialist and he told me its fine, and it starts after been left for a few days,  even though my multi meter says its a low voltage reading, it is a EFB exide battery.

[Breezy_Pete]

What made you suspect it might be unwell?

I mean before you did any investigation.

[paddywack1878]

i allways check the battery when i buy a new car, ive only had it a month, starts a few seconds after pressing the start button every time, 

[Breezy_Pete]

Ah, OK, good plan.

 

There are two factors that might mean it's fine.

The charging system on Start/stop cars actively avoids fully charging the battery.

Measuring in circuit, unless you've gone to significant trouble to ensure the car is completely 'asleep', you will always see a lower voltage than if the battery is disconnected from everything and left for a while

[Kenny R]

Stop/ start system batteries are normally only charged to approximately 80% by the system to allow for some capacity from the regenerative braking.

[paddywack1878]

i allways have the stop start switched off every time i get in because its a gimmick to me, and i hate it. I suppose the big test will be the winter but i have to get a oil service in about 4 months so i will ask skoda to test it then, but they will probably say the same as my local specialist.

[Breezy_Pete]

The charging system will still not charge it up fully even if you always disable S/S.

 

[paddywack1878]

4 minutes ago, Kenny R said:

Stop/ start system batteries are normally only charged to approximately 80% by the system to allow for some capacity from the regenerative braking.

kenny the place i went to told me its working

 

6 minutes ago, Wino said:

The charging system will still not charge it up fully even if you always disable S/S.

 

Oh ok wino, thats interesting mate.

[paddywack1878]

I forgot to mention in start stop traffic  today in 24 degree heat i switched the start stop off and low and behold it didnt stop the engine every time?

[Kenny R]

If the ac was on it wouldn’t.

[paddywack1878]

2 minutes ago, Kenny R said:

If the ac was on it wouldn’t.

nice one kenny, i will try the stop start tomorrow without AC.

[Kenny R]

34 minutes ago, paddywack1878 said:

nice one kenny, i will try the stop start tomorrow without AC.

The ac being on is only one item in a list of prerequisites for stop/start to operate.

[patrolman]

Smart charging systems only maintain the battery at around 80% this is to leave reserve capacity for regenerative braking as said before,

my concern here is a battery centre only using a multimeter to check a battery! Volts are nothing without amps  

Edited 1 June, 2021 by patrolman

[paddywack1878]

2 minutes ago, patrolman said:

Smart charging systems only maintain the battery at around 80% this is to leave reserve capacity for regenerative braking as said before,

my concern here is a battery centre only using a multimeter to check a battery! Volts are nothing without amps  

no mate that is my multimeter, the battery specialist had a proper all bells and whistles tester. 

[patrolman]

6 minutes ago, paddywack1878 said:

no mate that is my multimeter, the battery specialist had a proper all bells and whistles tester. 

Fair enough 

[paddywack1878]

Just now, patrolman said:

Fair enough 

no prob,  i just dont want to go out one morning and i get the old dead mans click, but what you guys mentioned about the 80% reserve capacity makes me a bit more confident 

[Alan_P]

I recently had similar concerns with my battery. I have a LUKAS LK-290 power management device feeding dash cams. It cuts the power at 12.6v so the battery never deep cycles. For years it gave an hour or two of recording after ignition off, but I noticed a few months back that the cams were not running on at all any more. This could have been going on for quite a while to be fair given the last year. It’s a Varta AGM that’s nearly 4 years old so just presumed it was on the way out or just needed a good charge due to lack of use.

I threw a multimeter on and the resting voltage was 12.2 which is not great. No warning lights, error codes or even the slightest hesitation at turnover. I had a friend put it on their workshop Bosch tester (see attached) and it came back as good but needing charged. It’s also putting out a very healthy 803 cranking amps (rated at 680) which explains why there is no hesitation and no dead cells. It’s levelling 11.84v on turnover with a minimum drop of 8.9v which is fine for a low charge state.

I gave it a two day charge with CTEK MXS 5.0 (recon enabled) and everything seemed fine, it didn’t detect any sulfation and no errors. I checked the resting voltage a day later without having used the car and it was a healthy 12.9v. I tested it again a day after using the car a few times through the week during daytime with no heavy load and the resting voltage was back to 12.4. For whatever reason, battery management is deciding not to fully charge the battery, not even to 80%. I told the system the battery was swapped out by changing the last digit, but it’s still the same. I notice the alternator initially goes to boost for around 30 sec of 14.6-14.8v then drops back to ~13v even after the battery reset. I just went out to test and resting voltage is 12.3v after not using it for 3 days so it's low but there doesn't seem to be a drain.

I understand this might be normal, but it didn’t behave like this before. I don't have figures from a few years ago, but I think the lack of dash cam run on indicates something is different. I can’t work out why management has decided to keep it at ~60% instead of 80-90% charged. I have always manually disabled start-stop every time I use the car and now wondering if it actually causes a problem.

Edited 1 June, 2021 by Alan_P

[paddywack1878]

Alen that last sentence has got me thinking, I think you might have stumbled across something, I always have the stop start switched off and its going to stay off, I really hate that function.  

[Alan_P]

I would be really interested in what resting voltage other owners get and if they use start-stop. I wonder if changing the temp or voltage threshold with VCDS would be better than manually disabling start-stop.

[Kenny R]

The thing is to get a true resting voltage from the battery, you either need to disconnect the battery and check a good few hours after charging. 
Or you need to connect your meter to the battery ( and place somewhere it can be read with bonnet shut) , close the bonnet, lock the doors, and leave for a few hours.

If you are checking the battery after unlocking the car opening doors etc, the fuel pump will have primed, interior lights come on and the car systems woken up, so you will not get an accurate reading.

[Alan_P]

It’s always at least a day after any charging before I take a reading. I leave the bonnet open, lock the car then leave it at least 30 min before testing. It might not be perfect, but I really don’t want to disconnect the battery.

[Breezy_Pete]

If you were to also flick the bonnet latch over after opening the bonnet (to make the microswitch in the latch register a closed bonnet) and before locking up and waiting 30 mins plus, you should see a proper 'asleep' reading.  Not sure how much if any difference this makes. Would be interested to know if you fancy trying it?

 

Remember to pull the bonnet release inside the cabin before trying to shut the bonnet afterwards though, otherwise it'll clang into the closed latch.

 

[J.R.]

It makes a big difference, initially there can be 200mA, it drops to lets say 60ish mA within a couple of minutes and then down to the basic quiescent current after 10 or 15 minutes on my vehicle, 30 minutes is a safe time to wait to be sure.

[Alan_P]

25 minutes ago, J.R. said:

It makes a big difference, initially there can be 200mA, it drops to lets say 60ish mA within a couple of minutes and then down to the basic quiescent current after 10 or 15 minutes on my vehicle, 30 minutes is a safe time to wait to be sure.

 

Do you mean with the bonnet open/closed or just in general? I will be able to check the comparison on my car in a few days.

[J.R.]

With the bonnet open but the latch closed so the vehicle would go into shutdown, easiest way to put a current meter in series with the battery & be able to read it without the danger of a closed bonnet cutting a lead & creating a short circuit.