Not sure if this is one of those "known" issues..... Have a 2018 Superb with 80,000km and in very good condition. Recently the battery died and the car is not sitting for more than a day or two but it does have shortish trips - maybe 15-20 km. After twice failing to start the car in the morning I checked the voltage and it was just over 12v. I charged up with decent charger and got it to 13v. It dropped to around 12.75 and stabilised so not great. The charging voltage was 14v+ so the alternator is charging.

After several charges overnight and finding low voltage readings I checked for leakage but only a few milliamps. I therefore replaced the battery yesterday and the car was taken out to reset everything. Voltage was 12.85v. This morning the voltage was 12.40V. Enough to start the car but something is wrong. Any ideas ?? Nothing is on as far as I can tell.

Run me through how youve checked for a battery drain and when working with drains youre gonna need to supply specific numbers as they are so small a few milliamps can make all the difference.

There is nothing wrong with your readings.

 

Your car has a micro hybrid battery charging system, designed to reduce fuel consumption by allowing recuperation of energy under certain conditions, e.g. braking.

 

In effect the system has a target state of charge of around 80% to allow energy recuperation. It will allow the battery to discharge lower, possibly as low as 60% and recuperate or charge at a later more fuel economic time.

 

To allow this the car is fitted with an EFB or AGM battery that can tolerate low states of charge specifically for this purpose.

 

State of charge (SOC) is tracked by monitoring current going in / out of the battery, a device integrated into the negative terminal connector on the battery as well as many other parameters battery voltage, battery temperature and monitoring of current used by consumers throughout the vehicle. The battery management system has the ability to vary the output of the alternator quickly and accurately to control the SOC.

 

When charging the battery externally with your charger, please be aware you need to connect the negative lead of the charger to the chassis tab and NOT the battery negative terminal (see manual) to avoid the battery management getting confused as you would bypass the current sensor.

 

When you check battery voltage you need to be aware of several things.

 

Immediately after charging, battery voltage will be elevated due to the phenomenon of surface charge. You need to allow an hour or so for this charge to dissipate and the voltage be measured.

 

When you open the car to open the bonnet, all the cars systems spring to life and a large current drain depresses the battery voltage. Make sure the car is closed and wait 10 mins for all the systems to go to sleep and the battery voltage to recover to a rest state before measuring.

 

As you can see below 12.4 volts represents approx 80% SOC which is bang on where it should be. (Use the Wet chart for EFB) Also note that voltages vary with temperature, so these voltages are only a rough guide

 

 

 

 

Edited 18 January, 20224 yr by xman

Assuming your car has stop/ start and therefore a micro hybrid / smart alternator charge system that will only charge and maintain the battery at around 80% to allow space to dump charge when on the overrun.

The voltage readings you have seem perfectly fine.

Edited 18 January, 20224 yr by Kenny R
Need to learn to type faster

1 hour ago, freddyuk said:

After several charges overnight and finding low voltage readings I checked for leakage but only a few milliamps. I therefore replaced the battery yesterday and the car was taken out to reset everything.

 

When replacing a battery, it is necessary to recode your vehicle to notify it that a new battery has been fitted to reset several parameters, State of Charge SOC, Health of Charge (HOC - remaining battery life to you and me), and any change of basic battery specs such as Ah rating, and if EFB or AGM is fitted. It is a simple procedure but requires a diagnostic tool capable of this. Not doing this can lead to issues and shortened (replacement) battery life. You must use an EFB or AGM battery, standard batteries are not suitable and will have a short life.

 

If changing from EFB to AGM or vice versa, battery coding is essential as they operate at different voltages and you will experience issues with stop/start and short battery life.

 

For information, from my long term measurements, the parasitic drain from my cars systems when everything is shut down/ asleep is around 10mA, however many subsystems wake up briefly from time to time and there are moments when it goes up to 60mA or more for maybe 30 seconds or so, so I reckon an average drain may be around 15mA. Of course there is battery self discharge on top, this will vary with battery age, temperature and SOC.

 

I wouldn't recommend disconnecting the battery to measure parasitic drain with a series multimeter. Risk of damage to your meter and the cars systems.

Edited 18 January, 20224 yr by xman

Thanks for all the info.

The battery is losing charge overnight so the car would not be able to start due to insufficient current. Fundamentally that is an unacceptable problem notwithstanding all the ECU issues and requirements.

I connected the charger to the negative ground of the body.

I checked the voltage after 4 hours of standing idle and the voltage had dropped in the battery too much.

I fitted a new battery with full charge in the evening and in the morning it was not fully charged going by the voltage reading.

Is that a car problem or a programming problem??

I am simply trying to find out if this is a known issue. It seems not??

 

 

 

 

I had a similar problem on my 2011 VW CC.  New battery fitted and coded.  Alternator refurbished.  And still had the same issue.  Local Auto Electrician traced it to be a fault with the amplifier for the stereo / radio head unit.  Apparently there are known faults with some amplifiers used by the VW group.

 

I used the following company to repair the amp:  https://www.amp-performance.de/en

 

Since then no problems,  

 

This is the issue I had:

 

 

 

Edited 21 January, 20224 yr by MunsterScot

@freddyuk you don't appear to have answered @ApertureS about how you measured the parasitic current? 

Did you just measure it once  there may be an intermittent fault?

Grab an assistant and try it this way, if it's not how you did previously 

https://www.briskoda.net/forums/topic/495243-quick-and-dirty-parasitic-current-measurement/?tab=comments#comment-5557920

 

5 hours ago, MunsterScot said:

I had a similar problem on my 2011 VW CC.  New battery fitted and coded.  Alternator refurbished.  And still had the same issue.  Local Auto Electrician traced it to be a fault with the amplifier for the stereo / radio head unit.  Apparently there are known faults with some amplifiers used by the VW group.

 

I used the following company to repair the amp:  https://www.amp-performance.de/en

 

Since then no problems,  

 

This is the issue I had:

 

 

 

This is interesting, any idea what gets replaced at this cost? Cause I don’t think it’s the amplifier as this costs around £1000

What happens is you send you amplifier to them.  They inspect / test it and let you know what the issue is.  If you agree to it they repair the amplifier and ship it back to you.  I had my one repaired approx. 12 - 18 months ago and it's still working fine with no power issues.

On 21/01/2022 at 13:11, MunsterScot said:

What happens is you send you amplifier to them.  They inspect / test it and let you know what the issue is.  If you agree to it they repair the amplifier and ship it back to you.  I had my one repaired approx. 12 - 18 months ago and it's still working fine with no power issues.

Ah sorry i thought it was an offical skoda TPI, its not, now im with you
 

Thanks all. Been busy. Will do the checks as advised and report back. The car has been starting with the new battery.

 

Any updates on this topic?