At 9:26 the battery voltage was 12.2v but appeared to have no trouble starting the engine at

9:29 14.9v engine running alternator charging

If you left it running until

10:05 got up to 12.6v engine stopped

surface charge dissipating until

10:06 12.4v

no data to see if this carried on back down to 12.2v

Data visible suggests the Battery is very low on charge.

The scanner says battery condition currently ok at 12.6v 10:05

Now you have the scanner I would charge the battery up with a charger that tells you it's done or for a good few hours

Negative charger lead to the body where the negative battery/bms lead goes

It should not drop to 12.4v that quick if it was fully charged in the beginning. Unless there is a big load on it whilst you did the above. But the being almost flat and allowing for surface charge dissipation results in 1/2 an hour are not enough.

Plug it in again starting with a charged battery.

You never answered how many miles the car had done before you got it. Just 4,000 miles since, it's important, if the car has sat untouched for six months of it's life the battery could be knackered.

1 hour ago, Stonekeeper said:

At 9:26 the battery voltage was 12.2v but appeared to have no trouble starting the engine at

9:29 14.9v engine running alternator charging

If you left it running until

10:05 got up to 12.6v engine stopped

surface charge dissipating until

10:06 12.4v

no data to see if this carried on back down to 12.2v

Data visible suggests the Battery is very low on charge.

The scanner says battery condition currently ok at 12.6v 10:05

Now you have the scanner I would charge the battery up with a charger that tells you it's done or for a good few hours

Negative charger lead to the body where the negative battery/bms lead goes

It should not drop to 12.4v that quick if it was fully charged in the beginning. Unless there is a big load on it whilst you did the above. But the being almost flat and allowing for surface charge dissipation results in 1/2 an hour are not enough.

Plug it in again starting with a charged battery.

You never answered how many miles the car had done before you got it. Just 4,000 miles since, it's important, if the car has sat untouched for six months of it's life the battery could be knackered.

I bought the car in August it was 14180 miles

Car now is 18466

It was a hire car for the 1st 10 months of its life.

I scanned it again with the obd eleven vag app this time and only bought up 1 fault?

I sensed there was something wrong with my battery and yes I could have started charging the battery or load testing it etc.. guys the car is under warranty. Just take it to the dealer and let them diagnose and sort for you.

16 minutes ago, whippersnapper said:

I sensed there was something wrong with my battery and yes I could have started charging the battery or load testing it etc.. guys the car is under warranty. Just take it to the dealer and let them diagnose and sort for you.

In the UK though the chances are they will charge for the diagnostic then charge it up and give you the car back.

Best to have done that yourself before taking it in.

9 minutes ago, Stonekeeper said:

In the UK though the chances are they will charge for the diagnostic then charge it up and give you the car back.

Best to have done that yourself before taking it in.

Sound like warranty has a different meaning in the uk then. Here in NZ they did everything with a smile, took my photo of the warning lights I had, gave me a free kamiq Monte Carlo for the day, washed my car (to be fair it was already clean) and charged nothing.

7 hours ago, Tonyduncan said:

Sorry

1st ans 2nd pic reasting voltage

3rd engine running

You can spend a week doing scans when a 10min trip to a battery place and a load test will give you the answer you are dancing around. Your pics are A Float level and C level with alternator working which means nothing to help your problem. To find if your battery is stuffed you can do the above suggestion or get someone to hold a meter across the terminals while you start the car. THAT is when the true state is shown as is when the heaviest load is put on it and a stuffed battery will dip down below operating level at that time , but can still show a reasonable float state .

Had a faulty 12v battery as wel early this year. Replaced it never seen the issue again. Battery was only 3,5 yo.

I find batteries tend to only last 4 years anyway. On my Subaru I had sudden failures so I just replaced them on a schedule

Which seems to me to be a potential avoidable waste of valuable metal resources.

I cannot be an exception if a modicum of battery maintenance is taken.

- 9 year old Moll EFB, always use stop/start, frequent short trips, yet the battery still tests as in good condition with better than 80% health report

17 hours ago, Exkiwi said:

You can spend a week doing scans when a 10min trip to a battery place and a load test will give you the answer you are dancing around. Your pics are A Float level and C level with alternator working which means nothing to help your problem. To find if your battery is stuffed you can do the above suggestion or get someone to hold a meter across the terminals while you start the car. THAT is when the true state is shown as is when the heaviest load is put on it and a stuffed battery will dip down below operating level at that time , but can still show a reasonable float state .

Thank you I will try the test i have a muilty meter battery is only 11 months old if no good will thay replace under warranty?

10 hours ago, Warrior193 said:

Which seems to me to be a potential avoidable waste of valuable metal resources.

I cannot be an exception if a modicum of battery maintenance is taken.

- 9 year old Moll EFB, always use stop/start, frequent short trips, yet the battery still tests as in good condition with better than 80% health report

Not sure what maintenance means. It’s sealed for life. The car was always garaged and in a moderate climate. I’m sure the biggest driver of longevity is the use case of the car only which you can’t standardise. A lot of short trips surely takes its toll. My motorcycles are all on battery tenders because they are used far less often. The batteries are extensively recycled anyway. It might just have been that car because I’ve never had anything like it before or since.

1 hour ago, whippersnapper said:

Not sure what maintenance means. It’s sealed for life. The car was always garaged and in a moderate climate. I’m sure the biggest driver of longevity is the use case of the car only which you can’t standardise. A lot of short trips surely takes its toll. My motorcycles are all on battery tenders because they are used far less often. The batteries are extensively recycled anyway. It might just have been that car because I’ve never had anything like it before or since.

My maintenance of sealed batteries, especially on these micro-hybrids, consists of regular condition and SOC tests, check of terminal connections, combined with occasional recharging to full SOC.

You should by now be aware that a micro-hybrids alternator will not charge the battery to 100% SOC, instead relying on energy recuperation to charge above 75-80% - especially with regular short trips - this can result in hard (non-reversable) sulfation of the plates, which will shorten battery life.

7 hours ago, Warrior193 said:

My maintenance of sealed batteries, especially on these micro-hybrids, consists of regular condition and SOC tests, check of terminal connections, combined with occasional recharging to full SOC.

You should by now be aware that a micro-hybrids alternator will not charge the battery to 100% SOC, instead relying on energy recuperation to charge above 75-80% - especially with regular short trips - this can result in hard (non-reversable) sulfation of the plates, which will shorten battery life.

I assume you are talking about the hybrid, I have a 4.5 RS

1 hour ago, whippersnapper said:

I assume you are talking about the hybrid, I have a 4.5 RS

The answer from AI as to why short trips drain a full battery and the possibility you will have to "maintain it" by trickle charging periodically to stop it going flat.

"How the smart charging system works

Instead of constant charging, a vehicle's Engine Control Unit (ECU) manages the alternator based on a variety of factors: 

• Battery state of charge (SOC): When the battery needs to be topped up, the system increases the alternator's output. Once the battery reaches a certain level, often around 80%, the ECU can reduce or stop the alternator's charging output to save fuel.

• Engine conditions: During acceleration, the ECU can temporarily reduce the alternator's load to provide more power to the drivetrain. When the car is decelerating or coasting, the ECU increases the alternator's output to maximize energy recovery, a process known as regenerative braking.

• Electrical load: The alternator's output is adjusted in real-time to meet the vehicle's electrical demands. When accessories like the headlights, air conditioning, and heated seats are on, the alternator is commanded to increase its output to prevent the battery from draining. 

Consequences for vehicle owners

This adaptive charging system has several notable effects:

• Less-than-full charge: Many vehicles with smart charge technology deliberately do not maintain a 100% battery charge level to maximize fuel savings. This makes it more likely for the battery to be in a state of partial charge.

• Sensitivity to short trips: Drivers who frequently make short trips may not give the alternator enough time to fully recharge the battery. Over time, this can lead to sulfation, a process that diminishes the battery's capacity."

3 hours ago, whippersnapper said:

I assume you are talking about the hybrid, I have a 4.5 RS

No, a Micro-Hybrid - as yours presumably is.

Edited 12 October, 202512 Oct by Warrior193
correction

On 12/10/2025 at 21:36, Warrior193 said:

No, a Micro-Hybrid - as yours presumably is.

Interesting. This is a term I’ve never heard of. Had to look it up. So far everyone I’ve asked has never heard of it either.

1 minute ago, whippersnapper said:

Interesting. This is a term I’ve never heard of. Had to look it up. So far everyone I’ve asked has never heard of it either.

It is what the Mk3 is classed as - starting from around 2015.

On 12/10/2025 at 16:45, Stonekeeper said:

The answer from AI as to why short trips drain a full battery and the possibility you will have to "maintain it" by trickle charging periodically to stop it going flat.

"How the smart charging system works

Instead of constant charging, a vehicle's Engine Control Unit (ECU) manages the alternator based on a variety of factors: 

• Battery state of charge (SOC): When the battery needs to be topped up, the system increases the alternator's output. Once the battery reaches a certain level, often around 80%, the ECU can reduce or stop the alternator's charging output to save fuel.

• Engine conditions: During acceleration, the ECU can temporarily reduce the alternator's load to provide more power to the drivetrain. When the car is decelerating or coasting, the ECU increases the alternator's output to maximize energy recovery, a process known as regenerative braking.

• Electrical load: The alternator's output is adjusted in real-time to meet the vehicle's electrical demands. When accessories like the headlights, air conditioning, and heated seats are on, the alternator is commanded to increase its output to prevent the battery from draining. 

Consequences for vehicle owners

This adaptive charging system has several notable effects:

• Less-than-full charge: Many vehicles with smart charge technology deliberately do not maintain a 100% battery charge level to maximize fuel savings. This makes it more likely for the battery to be in a state of partial charge.

• Sensitivity to short trips: Drivers who frequently make short trips may not give the alternator enough time to fully recharge the battery. Over time, this can lead to sulfation, a process that diminishes the battery's capacity."

A very good and true description of how it all works.. Could I just add that with the battery at 80% it gives headroom for regenerative charging when car is "floating" as in going downhill with no power applied

When I start the car after the dashboard light check and thay all go out if I don't start the engin the yellow battery light comes back on and stays on till I start the engine is this normal or a problem.

That is normal - the battery is being discharged while the engine isn't running.

On 11/10/2025 at 09:49, Warrior193 said:

Which seems to me to be a potential avoidable waste of valuable metal resources.

I cannot be an exception if a modicum of battery maintenance is taken.

- 9 year old Moll EFB, always use stop/start, frequent short trips, yet the battery still tests as in good condition with better than 80% health report

Sometimes i wonder about battery testers. My 18 month old battery tests anything from 50%-70% ( depending on it’s mood) with a “replace” report. However it performs perfectly and so does the start stop.

1 minute ago, Micky 32 said:

Sometimes i wonder about battery testers. My 18 month old battery tests anything from 50%-70% ( depending on it’s mood) with a “replace” report. However it performs perfectly and so does the start stop.

Unless the exact same conditions apply at each time of testing, you can reasonably expect some variation - SOC, ambient temperature, surface charge, status of Canbus modules, etc. will all have some effect.

The most reliable test is to fully charge battery, allow sufficient time for any surface charge to dissipate, check that all canbus modules have entered sleep mode, then apply test.

Important to note that the battery will virtually never be at fully charged state if solely charged by vehicles alternator. (for Micro-Hybrid)

3 minutes ago, Warrior193 said:

Unless the exact same conditions apply at each time of testing, you can reasonably expect some variation - SOC, ambient temperature, surface charge, status of Canbus modules, etc. will all have some effect.

Yeah, i always make sure everything is shut down and take note of the soc. You can get a 100 amp difference if your soc is 12.45v vs 12.70. My battery is a 700 amp en. At 12.45v it reads 500 amps. At 12.6-7 it reads around 600 amps en ( good battery, recharge).

Comparing to other batteries that are the same helps. A friend has the same battery in his VW but a year older. I tested both at the same voltage 12.45. Mine read 500 amps “ replace” and his read 636 amps “ good battery”. His engine and battery was cold but mine was hot with a warm battery.

4 hours ago, Micky 32 said:

My 18 month old battery tests anything from 50%-70% ( depending on it’s mood) with a “replace” report. However it performs perfectly and so does the start stop.

My near 4 year old battery was left unused for 10.5 days recently and the voltage reading was 11.9v before attempting starting the car. (mentioned in another thread, re- charging)

It started absolutely normally. I believe that 11.9v is around 40% charge (AGM/EFB), though another mention was 25%.