Strange battery charging voltage?

[CupraTOC]

I have a 2017 Leon ST (1.8TSI). Had the obdeleven on live data whilst driving and noticed that the alternator seems to charge around 13.2V whilst using gas pedal and if I lift off goes up to a 14.4v charge. Same pattern everytime.

I know there is some smart electronics in these newer cars but is this normal? I'm used to older cars giving the battery a constant charge of just over 14v.

 

[RUM4MO]

Absolutely, the charging plan nowadays is to minimise charging under normal conditions unless the battery really needs it, and leave the charging until it comes by way of "wasted energy" ie when the car is on the over run and braking.

I think the aim is to always have some spare capacity for "dumping free charging" into the battery which means a well charged battery will normally be at max at 75>80% charged. It will always be able to restart the car though.

 

[CupraTOC]

Absolutely, the charging plan nowadays is to minimise charging under normal conditions unless the battery really needs it, and leave the charging until it comes by way of "wasted energy" ie when the car is on the over run and braking.

I think the aim is to always have some spare capacity for "dumping free charging" into the battery which means a well charged battery will normally be at max at 75>80% charged. It will always be able to restart the car though.

Got ya! So that's why when I'm playing with obd with just ignition it doesn't take long before it shows battery full to discharging. May also explain why there seems to be a common failure of batteries within a two to three year from new as constantly only charging up to 80% capacity cannot be too good for the battery long term.

 

[RUM4MO]

Actually, these cars with start/stop etc should only ever get fitted with EFB batteries or AGM batteries and it is claimed that both can tolerate that sort of use.
Where the proper abuse comes in is when a car is used only frequently and for short journeys.
My wife's 2015 VW Polo 1.2TSI 110PS gets used at least twice a week on 10+single journeys, during lockdown it was connected up to a smart charger - CTEK MSX 5, and its battery still checks out as being quite healthy - I have a CTEK battery tester and that gives a "capacity" measurement in CCA. My car is a 2011 Audi S4 and it tends to be grossly underused but is always connected to another CTEK 5 test and charger - its battery is now over 10 years old and still appears/tests as being quite healthy, although at this age I've bought a new battery as 10 years in my world is good enough and I don't want to end up with battery failure if and when away from home with that car.
The charging setting will be slightly different for an EFB and a AGM and once a change of battery is logged into the car, including battery type, that will get taken care of.

 

[CupraTOC]

Actually, these cars with start/stop etc should only ever get fitted with EFB batteries or AGM batteries and it is claimed that both can tolerate that sort of use.
Where the proper abuse comes in is when a car is used only frequently and for short journeys.
My wife's 2015 VW Polo 1.2TSI 110PS gets used at least twice a week on 10+single journeys, during lockdown it was connected up to a smart charger - CTEK MSX 5, and its battery still checks out as being quite healthy - I have a CTEK battery tester and that gives a "capacity" measurement in CCA. My car is a 2011 Audi S4 and it tends to be grossly underused but is always connected to another CTEK 5 test and charger - its battery is now over 10 years old and still appears/tests as being quite healthy, although at this age I've bought a new battery as 10 years in my world is good enough and I don't want to end up with battery failure if and when away from home with that car.
The charging setting will be slightly different for an EFB and a AGM and once a change of battery is logged into the car, including battery type, that will get taken care of.

Well my original factory fitted battery died after two years and have read many issues with the factory fit batteries failing early. Have now fitted a Halfords advanced AGM stop start and changed the setting in OBDeleven to glass mat. So far so good and hopefully this will last a fair few years as car gets used on 12 mile journey daily .

 

[Mo_86]

Reviving this old thread instead of starting another,
I recently changed battery on my car to agm, got it coded to fleece etc.
I bought a cheapo cigarette lighter voltage meter and with engine off its showing 12.2v which i believe is ok but when the car is on idle it'll go to 14 then drop and stay on 13.1.
It barely changes when driving and did once drop to 12.7v.
Do i have an alternator issue?

 

[TheSwede]

Test - on idle: Turn on high beam, seat heating, rear window heating, passenger compartment fan full load and wind screen wipers. Then the altenator should charge with over 14 v.

 

[Mo_86]

Test - on idle: Turn on high beam, seat heating, rear window heating, passenger compartment fan full load and wind screen wipers. Then the altenator should charge with over 14 v.

Thanks for your reply, tried this, don't have heated seats so put the heated mirrors on, it went up to 13.8 then maintained 13.4v

 

[TheSwede]

Hmmm. I agree, confusing.

 

[RUM4MO]

I hadn't thought of using heated seats as an extra load, maybe because my car (B8 S4) does not have them, though my wife's 2015 VW Polo 1.2TSI 110PS 6MT does, so I'll try that today to see if it makes much of a change to the voltage "seen" at the 12V DC power socket.

Both my cars, a 2011 Audi S4 6MT and the 2015 VW Polo 1.2TSI 110PS 6MT have had new batteries fitted over the past few years, the S4 got a new same size AGM really just because it was 10 years old, the 2015 VW Polo 1.2TSI got its original EFB replaced with a "next size up" AGM, again as the car was now over 10 years old. So neither original battery was causing any problems in either car. Both car's BMS were updated to reflect the new battery in the S4 and the new but different type and size of battery in the VW Polo 1.2TSI.

Most of the time, especially in cold weather, over a typical 10 > 20 miles journey, the voltage at the 12V DC power sockets is close to the 14.9V level, although I noticed that the voltage on the Polo did drop quickly during the recent " warm spell" of weather.

It does seem to still be a bit confusing, I thought that it would have become very easy to guess what the voltage would be during a normal journey - but there again, what is a normal journey, I have found that the Polo, especially with its original EFB battery fitted, would frequently end up with "auto stop" disabled at the end of a smooth 10 miles run - and I've put that down to the smooth/slow driving due to rush hour, but flow well, traffic, and I had ended up with the car, after initially re-charging the battery, was now "harvesting" that charge and when I had stopped at the first set of lights, it was not in a position to enable "auto stop". That might just be due to me driving the car in a way that is not representative of a typical driver - I think that frequent accelerating and coasting-braking is expected, and sometimes that is not how I drive, typically when this happens, the "average journey MPG" is extremely high - so yes, as most of us already know, "auto stop/start" can sacrifice economy for something else!

 

[nd-photo.nl]

If you want to log the behaviour, add a battery monitor to it. My Leon fluctuates between 13.x and 15 volt. I did not check when its 13 and when its 15, but I see it happening on my turbo/voltage gauge.

 

[tracktoy]

If you have OBD11 then under control unit 01 / live data/ use Voltage terminal 30 and or Voltage terminal 15 and if you put this into a chart you can record in real time the changes.

 

[Mo_86]

If you have OBD11 then under control unit 01 / live data/ use Voltage terminal 30 and or Voltage terminal 15 and if you put this into a chart you can record in real time the changes.

Checked on a friends obd11 today, the battery option part was showing 13v and in good condition, then when turning heat etc it showed 13.4v and status changed to charging.