12V battery problem?

[Pascal]

I bought an Mg HS PHEV on 21 nov 2025. Yesterday, it was dead. I had charged it overnight, but in the morning, I couldn’t unlock the doors, nor could I unplug the charging cable. I contacted the dealer 2km away, but he refused to send a technician. I had to Vaal the MG road assistance. They came and told me the 12V battery was faulty. Immediately went to the dealer. He checked the car and told me there was nothing wrong with this battery. If I wanted a new one, I would have to pay for it myself. He didn’t bother checking what caused the total breakdown of the car and that was it! There could be some kind of leak in the electric circuit, or the alternator could be malfunctioning. Has anyone had this kind of problem and how was it fixed?

 

[HStrophyPHEV2025rc]

Yes, others have reported a flat 12v battery in this forum. I suggest you read these threads:

• MG HS Hybrid battery drain
• Battery drain again

From what I can tell, it seems that some cars have faulty infotainment screens where the backlight does not switch off overnight (they look 'grey' not truly black at night) so they constantly draw power.

 

[Totti1001]

As already mentioned, the first models had faulty displays that were constantly lit.
In my case, it was the light/rain sensor next to the camera. It was constantly heating up, melting even 10 cm of thick snow. The 12 V battery was empty after three days.
The car was then in the workshop for seven days. Apparently, only the software for the BCM was reinstalled. I can't say whether that was really the reason, but since then the voltage of the 12V battery has remained stable. V

 

[Watty MG]

I had a dead car a couple of weeks ago after its annual service. Called out MG assist the battery was at 3 volts! He jumped the car from under the bonnet and it started fine all came back to life. Put the battery on charge for a few hours next morning same again at 3 volts. The battery was a 2 year old Bosch, not the original. The AA guy suggested a new battery. I fitted it on the Friday flat again by Monday. I got an appointment with the garage who did the service, for the next day. I left it on charge until the following morning started ok and drove to the garage. They confirmed my diagnosis that there was a 2 amp continuous discharge even with the car locked. They did a BCU (same as BCM above?) reset and I have had no more problems.
My car was registered February 2021

 

[TallboyKeith]

Sounds like what I had, a module not shutting down and draining the 12V battery. Parasitic Battery drain. I cured it by getting a refund on the car and going elsewhere. You have my sympathy. It wasn't a bad battery it was the parasitic module draining it. The battery charged and held the charge when off the car.