2025 Leon 1.5 eTSi MHEV DSG - 12v battery warnings

[oldglosracer]

Hi there,

What's the issue with the 12v battery charging on the 1.5 eTSi MHEV?

We keep getting warnings on the dash, 12v battery low, then followed by 12v battery critical turning off infotainment etc.

Is there a software update for it?

We've got it booked in next week at the dealership, but I'd like to have some information to give them, as sometimes they don't bother to check for technical bulletins.

Thanks

Rich

 

[oldglosracer]

Car is on the 2632 update

 

[NotApplicable]

So far, I have only ever seen those sorts of messages when the auxillary belt is a bit slack and not driving the alternator properly.
There may, of course, be another software specific issue i dont know about....

 

[oldglosracer]

So far, I have only ever seen those sorts of messages when the auxillary belt is a bit slack and not driving the alternator properly.
There may, of course, be another software specific issue i dont know about....

Thanks. Not even sure it has an alternator, maybe just a starter generator connected to the 48v battery.

 

[James_R]

There's a starter generator that starts the engine and charges the 48v battery. No starter motor.

There is a software update package available - PV4+KD that should resolve these issues. Once completed, the infotainment software version will rise from 2632 to 2768.

 

[oldglosracer]

There's a starter generator that starts the engine and charges the 48v battery. No starter motor.

There is a software update package available - PV4+KD that should resolve these issues. Once completed, the infotainment software version will rise from 2632 to 2768.

Thanks @James_R if I send you my VIN can you check it?

 

[oldglosracer]

The car has been in at Mon Motors Gloucester today. They report the battery is faulty and it will be replaced under warranty.
Not sure if they mean 12v or 48v, and no mention of the software update.

 

[oldglosracer]

12v battery is being replaced.

 

[oldglosracer]

Key Details Summary
Reported Issue: 12V battery fault light/warning displayed on the dashboard.
Diagnosis: A Guided Fault Finding (GFF) diagnostic test was conducted. The battery capacity/health came back at under 80%, indicating a failed battery.
Resolution:
Replaced the failed 12V battery with a new one.
Coded/programmed the alternator output/battery management settings per Technical Product Information (TPI) guidelines.
Verified that the alternator was charging the new battery properly

 

[Tell]

Hybrids seem to have issues with their batteries... long reported. They arent suppose to get a proper charge on the 12v side since people ride anout on the 48v battery. Well that's the story. But battery faults on the 12v side are quite common these days... so it seems. May be the software updates resolve the 12v battery getting a good charge ?.

 

[James_R]

The only thing the 48v battery does is start the engine via the starter/generator. It produces no additional engine power and doesn't propel the vehicle. The 12v battery is charged via an invertor that drops the 48v down to 12v(ish) from the 48v battery.

Poor battery care and substandard quality components are the most common cause along with software on earlier vehicles.

 

[Tell]

Always go I've heard this before. Trusty heavy duty diesel battery here. . None of this fangle stuff.

 

[Tell]

Ah

Repeated 12V Electrical Issues on CUPRA Leon 2024 – Anyone

Hey everyone, I wanted to share my experience with my CUPRA Leon 1.5 eTSI 150 CV DSG (2024 hybrid) and see if anyone else has faced something similar. My car has suffered from repeated 12V electrical issues — basically, the vehicle refuses to start. It’s currently on its fourth repair visit...

www.seatcupra.net

So it doesn't get a charge. We had a hybrid stuck across the road outside once. Visitor to the neighbour.... said they would never get a hybrid again and changed it. Ditto the guy at the bottom of the road... oh I've got rid of it. They were not Seat / Cupra cars.

 

[James_R]

I get the impression that the "mild hybrid" 48v system was a gimmick to allow the group to class vehicles as hybrids.

They offer no benefits over the non hybrid 1.5TSI engine and the tax cost was the same for the mild hybrid and non hybrid.

The 48v system starts the engine, charges the 48v battery when the engine runs and offers regenerative braking. It can't propel the vehicle or offer a power boost.

The charge flow is:
Starter/generator > 48v battery > invertor > 12v battery. The system can be charged backwards through the 12v system but the 48v contacts need to be closed and the charger needs to be capable of offering up to 100amps of current. It still doesn't offer any benefit unless either battery has become discharged.

The 1.4/1.5TSI hybrid is a completely different powertrain altogether.

 

[Tell]

Well I'd go straight to an EV than tow an ICE motor around... got a relative with a mild hybrid. Bit quirky as you described.

 

[James_R]

The actual hybrid powertrains are very good now, however you'd never know you had a mild hybrid from VWG as it does very little im terms of vehicle use, until part of the system fails and it costs a fortune to replace the parts.

On the Audis the 48v system can move the vehicle around at very low speeds for the likes of carpark maneuvering.

 

[Major]

I also drive a 2025 1.5etsi Seat Leon, also had issues with the battery discharging and @James_R suggested to go to the dealers so they update the car's software to "PV4RC", I would assume "PV4+KD" is newer, can you share what does it improve?
I wonder if it can fix the annoying issue where if the front windows are opened and I press the close button, they go down instead of up - this happens twice at the 3rd try they go up but I need to hold the button. The dealer said it's a common fault, but there was no software fix for it at the time.

As for the 48V system, I heard it decreases the lag when you press the accelerator from a standing start and one of the biggest downsides is a "2 step breaking pedal", where you put your foot on the break, a certain stopping force is applied, the regenerative breaking stops at some point close to a stop and you loose 20-30% of breaking power and you are not expecting it ...

P.S.
At the dealers I got my 12V battery replaced + they updated the car's software to PV4RC - I don't experience discharging issues anymore.