Vehicle charging all over the place

[AndyBen]

2020 Skoda Octavia 1.6 Diesel Est.  Classic symptoms of no charge at idle - 12.5V showing on meter - will rise to 13.4 if heater, air con etc put on but whilst driving output fluctuates between 12.5 - 13.4 and 15v.  Battery constantly becoming flat so battery changed (wasn't holding charge) - like for like battery (start stop compliant) fitted.  No change - symptoms pointed to alternator (regulator) so that has been changed!  Now £500 later and still the same!  What could it be as it is driving me nuts and expensive and I need to get mobile for work!

[Breezy_Pete]

Sadly that variable charging voltage is exactly what you should expect from the alternator in a VW group car with start/stop, so you probably just scrapped a working alternator.

The voltage varies to try to match supply and demand on the system.

When the new battery was fitted, was the car's battery monitor module re-coded to 'know' about the change?

[Stonekeeper]

I think you may need to investigate what is draining the battery, maybe overnight..

 

 

Anything plugged into the 12v sockets, one may be permanently live (boot?)

 

Is the light in boot on when boot closed etc.

 

Is the stop/start working?

 

Do you travel far?

Edited 5 April by Stonekeeper

[AndyBen]

 There is nothing remaining plugged in to any 12v socket.  Stop / Start does work (though not always as depends on battery status).  It would be really helpful to know if this is indeed the way that this model Skoda should operate as it seems bizarre that at idle the voltage reads 12.5 (you would expect 13.5v steady in old money) yet it does raise to 13.5v if you put the heater on etc and can peak at 15V - anybody else experienced this or confirm it is just the way it is!

 

Many thanks

[ords]

1 hour ago, AndyBen said:

 There is nothing remaining plugged in to any 12v socket.  Stop / Start does work (though not always as depends on battery status).  It would be really helpful to know if this is indeed the way that this model Skoda should operate as it seems bizarre that at idle the voltage reads 12.5 (you would expect 13.5v steady in old money) yet it does raise to 13.5v if you put the heater on etc and can peak at 15V - anybody else experienced this or confirm it is just the way it is!

 

Many thanks

You're putting a demand on the battery and the alternator is just doing its job. With no demand the altenator is basically idle. That's my reasoning.

[Breezy_Pete]

Read this:

 

Energy management.pdf

[Graham Butcher]

When I picked up my new to me car, in June last year, the battery in it was all wet on top and rather tired looking, so I replaced it with the one I took from my scrapped car which was brand new in November 2022 (replaced then under a 3-year warranty), and the voltmeter in my car used to show between 12.5 to 14v while driving. The last 3 weeks, the car alarm has been going off about 3 to 4 times a day at random times of the day and night. One of the trigger points for car alarms is, believe it or not, low battery voltage, but the car never failed to start or showed any other symptoms until this Monday when I went to go to a family meal out to celebrate my son's 41st birthday and also my Mother in Laws 93rd birthday and I was not even able to unlock the car, the battery had died overnight.

 

I tested it and it showed just 4v, so my son had to come and pick us up and after the meal took me to purchase a new battery. Battery fitted, no more random car alarms and the voltmeter is doing exactly as @Breezy_Pete said so I think you have just thrown away a perfectly good alternator.

[PetrolDave]

3 hours ago, AndyBen said:

 There is nothing remaining plugged in to any 12v socket.  Stop / Start does work (though not always as depends on battery status).  It would be really helpful to know if this is indeed the way that this model Skoda should operate as it seems bizarre that at idle the voltage reads 12.5 (you would expect 13.5v steady in old money) yet it does raise to 13.5v if you put the heater on etc and can peak at 15V - anybody else experienced this or confirm it is just the way it is!

That voltage varition is 100% normal on an Octavia 3 - it's how the micro-regenerative braking system works.

 

Nothing to worry about in any way.

[AndyBen]

Update and hopefully closure!

 

I am clearly old school and acknowledge it publicly but this update is to make anyone else out there aware if they have the same vehicle or same system.  @Breezy_Pete thank you for the PDF Eng Management System doc - makes sense and shows me how out of date I am with technological progress in the automotive world!  Thank you to all other contributors!

 

Nub of the issue - yes the old battery was shot (and replaced) and yes I have changed an alternator that I now don't think was necessary - my bad and expense - ouch!  However, despite a number of other forums talking about 'no need to tell the system' when you change the battery - you DO.  Once the system was informed about the new battery - done by a mobile diagnostic chap with his techno wizardry, the system is now charging perfectly well at idle etc.  Failure to do this and your system will continue to charge your new battery at the same rate as your failing one which, although won't be evident, will screw your new one pretty quickly with no apparent signs through warning lights etc. Consider deactivating your start / stop if possible - apologies to the environment as it does also shorten your battery life somewhat,

 

Moral is - accept that I am getting old and sometimes it is better to pay someone with the right gear and up to date knowledge than trying do it yourself!

 

Best wishes to all and thanks again - now to manage telling the wife how much I've spent in the last week - oh boy!!! 

[AGFalco]

4 hours ago, AndyBen said:

now to manage telling the wife how much I've spent in the last week - oh boy!!! 

Just tell her while you are driving her to somewhere she REALLY wants to go. 😮

 

Thanks. AG Falco

[J.R.]

8 hours ago, AndyBen said:

Failure to do this and your system will continue to charge your new battery at the same rate as your failing one which, although won't be evident, will screw your new one pretty quickly with no apparent signs through warning lights etc

 

No it won't, screw your new battery that is, did that nonsense come from the guy that did the recoding?

[ords]

13 hours ago, AndyBen said:

Update and hopefully closure!

 

I am clearly old school and acknowledge it publicly but this update is to make anyone else out there aware if they have the same vehicle or same system.  @Breezy_Pete thank you for the PDF Eng Management System doc - makes sense and shows me how out of date I am with technological progress in the automotive world!  Thank you to all other contributors!

 

Nub of the issue - yes the old battery was shot (and replaced) and yes I have changed an alternator that I now don't think was necessary - my bad and expense - ouch!  However, despite a number of other forums talking about 'no need to tell the system' when you change the battery - you DO.  Once the system was informed about the new battery - done by a mobile diagnostic chap with his techno wizardry, the system is now charging perfectly well at idle etc.  Failure to do this and your system will continue to charge your new battery at the same rate as your failing one which, although won't be evident, will screw your new one pretty quickly with no apparent signs through warning lights etc. Consider deactivating your start / stop if possible - apologies to the environment as it does also shorten your battery life somewhat,

 

Moral is - accept that I am getting old and sometimes it is better to pay someone with the right gear and up to date knowledge than trying do it yourself!

 

Best wishes to all and thanks again - now to manage telling the wife how much I've spent in the last week - oh boy!!! 

I'm on my original battery and S/S is always used, so have to disagree with your statement about a shortened battery life.  I go along with your other point re coding.

[PetrolDave]

22 hours ago, AndyBen said:

Failure to do this and your system will continue to charge your new battery at the same rate as your failing one which, although won't be evident, will screw your new one pretty quickly with no apparent signs through warning lights etc.

Initially it will continue to charge the new battery like the old one but it will soon learn that the battery SOC changes differently and adapt to the new battery. Coding just starts this learning process immediately.

[J.R.]

And in either case it will not destroy either the old or the new battery.

[Breezy_Pete]

It wasn't clear to me from the original post whether the new battery was actually giving any trouble or not.

Seemed more like the unexpected charging voltages were giving the OP the (false) impression that there was a residual problem. 

[J.R.]

That's how I read it too Pete, old battery going flat, new one fitted but no change to (correct) charging voltages.