I've been getting a warning that the 12V battery was low and the car clearly goes into some sort of energy conservation made, whereby it disables the interior lights and infotainment.

I assumed this battery was nearing its end although this surprised me a bit as I didn't think it was that old.

I ran the car to a local independent specialist who plugged it in and noticed the (after market) battery that was in had not been coded right but also tested the battery and noted it was at 95% and was at 12.2V. They cleared the error, coded the battery and all seemed fine - no charge because they are brilliant and lovely.

That lasted about 2 more drives. I now intermittently get this 12V Low warning, when I switch off after a journey with all the effects noted above.

Anyone got any bright ideas?

I am reluctant to get a new battery as the current one is clearly pretty healthy.

Thanks

11 minutes ago, Skodaddy18 said:

noted it was at 95% and was at 12.2V.

I don't understand the 95% what did they say that was because 12.2v is around 50% charged. Fully charged would be 12.6v or higher depending upon time checked

Oh sorry, to be fair that was me glancing at the machine and I may have misread it. I definitely saw battery health / charge whatever that is, at 95%. It's the intermittent nature of it I find odd.

At 12.2 volts, that 95% reading can only be battery Health - not SOC.

Was the battery load tested under a high-rate load?

Do you do a lot of relatively short runs?

What is the battery terminal voltage with the engine running?

Thanks - not sure what "high rate load" refers to? They had the lights on, fan, air con on - is that the load you are talking about?

I do do quite a few school runs which are short - but also did a solid 1000 mile trip over half term (including two 350 mile runs) and it made no difference.

If it currently 12.2v charge the battery up with the correct charger, then the next day check the voltage, after that the next step is to check the voltage as someone starts the car and see how low it goes and how quick it recovers.

If the vehicle's BMS (Battery Management System) indicates a low charge level, the battery can be replaced in 90% of cases.

59 minutes ago, Skodaddy18 said:

Thanks - not sure what "high rate load" refers to? They had the lights on, fan, air con on - is that the load you are talking about?

I do do quite a few school runs which are short - but also did a solid 1000 mile trip over half term (including two 350 mile runs) and it made no difference.

That sort of load can give some indication but is not usually high enough to be conclusive - a high load test will be in the region of 50 to 100 Amps minimum - measuring the battery terminal voltage while the engine is being cranked can give a fair idea of condition, but is limited to a short duration test unless the engine is prevented from starting.

Edited 16 November, 202516 Nov by Warrior193
typo

Was the battery BMS adaptation (coding) error corrected before or after the half-term holiday trip?

Is the correct type of battery (EFB or AGM) fitted?

Edited 16 November, 202516 Nov by Warrior193
question

Thanks all - amazed how knowledgable everyone is! The BMS error was corrected after the half term trip.

I'd suggest checking the alternator output by testing the battery terminal voltage while the engine is running (should be something over 14 volts) - if that's ok, have the battery fully charged and tested again.

Being a bit old school, I'd go with a volts drop test under load to check continuity on both supply and earth circuits . I'd be looking for under 0.5 volts .

As above , 12.2v is a 50% charge so that(95%) must be battery health ?

1 hour ago, Warrior193 said:

I'd suggest checking the alternator output by testing the battery terminal voltage while the engine is running (should be something over 14 volts) - if that's ok, have the battery fully charged and tested again.

provided it is requested via the LIN

35 minutes ago, Cairus said:

provided it is requested via the LIN

Which it should, if battery voltage is down to 12.2 as stated by OP.

Just because the open-circuit voltage is 12.2V doesn't mean that the LIN bus is sending 100% of the alternator's power request; it doesn't mean that it's charging the battery at 14.XV.

18 hours ago, Warrior193 said:

I'd suggest checking the alternator output by testing the battery terminal voltage while the engine is running (should be something over 14 volts) - if that's ok, have the battery fully charged and tested again.

When running the battery voltage can be as low as 12.5V - if the BMS determines that the battery has reached 80% SOC.

It's usually only over 14V for a short period after starting the engine, or when on trailing throttle (as a form of micro hybrid).

18 minutes ago, PetrolDave said:

When running the battery voltage can be as low as 12.5V - if the BMS determines that the battery has reached 80% SOC.

It's usually only over 14V for a short period after starting the engine, or when on trailing throttle (as a form of micro hybrid).

This is also my understanding of the BMS and EFB AGM battery technology as an operating strategy.

Worst thing that can happen to a sealed efb or agm is over charging.

Stop/start circuitry monitors for 80% if the car is below it disables.

BMS aims to maintain above 80% but will not go to 100% because that would leave no headroom for engine braking regeneration.