12 V Battery Charging System Fault

[DoctorWolf]

Hi all

Apologies if this has been covered elsewhere. I was driving my MG4 Trophy LR (73 plate) and noticed that the red battery light was on and the charge read 11.9V . It slowly discharged before I then got the 12V battery charge system fault warning. It kept going down until it reached 10V and then suddenly it was back to 13.7V and warnings cleared. I was passing a garage and they checked the battery. It was was at about 12.5V and had 65% health. As I restarted, the red battery warning light came back on. I was near home and managed to get there just as the battery appeared to discharge and multiple warnings came on before it eventually shut down. I was able to lock the car and then power on and the charge level said 13.7V again so I could actually get it in through my gates and off the road. Powered off and then on again at home and red battery light back on. Any thoughts and advice greatly appreciated. Worried about trying to get the car anywhere to check it out without it shutting down.

Thanks!

 

[Martinonline]

This is my experience of your problem from 2024, though not as bad as yours:

My Trophy showed a low-voltage battery charging problem when I went to drive it yesterday. The car was showing 11.9V. I've had this before and then after a quick power on and granny-charge the error disappeared. However this time I could not cancel it, a quick drive saw the voltage drop to 11.7V. I am away from home but tried to charge with the hotel's 16amp EVSE. Car would not connect and usual fixes failed. Drove to a 50kW charging station and tried DC but again no joy. (100% level set, no schedules.)

Back at the hotel the battery level was 11.5V. So I unpacked my Noco battery booster and connected it to the battery (with clicking (relay) noises coming from a unit to the right of the battery). The battery reached 14.2V and after I disconnected the booster went to 14.3V. I shut down the car and left it overnight during which time the battery went down to 12.5V.

This morning I powered up the car and it showed no faults and the expected 14.2V charging level. I connected it to the hotel's EVSE and it started charging with no issues.

I don't know if the fault would have corrected itself without the booster but I am just grateful to those posters who recommended carrying one.

Your voltage when the car is powered up seems to be on the low side and perhaps this is associated with a problem that is restricting power to the low power circuits leading to a drain from the 12V battery. We know that the car is supposed to keep the 12V battery topped up but this is the first time its action has been seen 'in the wild'.

Do you have a battery booster? Have you ever seen the battery voltage higher than 13.7V?

You could try disconnecting the battery, leaving it for 10 minutes then re-connecting to see if this 'hardware' reset works. See the Wiki on the actions required to be undertaken after a disconnect.

 

[OriginalBigAl]

Do you , or a neighbour/ friend have a Multimeter so you can keep an eye on the real battery voltage . It may be a problem with the 12 v charging system or how its just reported. Check the the battery terminals are clean and dry and the clamps are tightened up , for starters.

 

[DoctorWolf]

This is my experience of your problem from 2024, though not as bad as yours:

My Trophy showed a low-voltage battery charging problem when I went to drive it yesterday. The car was showing 11.9V. I've had this before and then after a quick power on and granny-charge the error disappeared. However this time I could not cancel it, a quick drive saw the voltage drop to 11.7V. I am away from home but tried to charge with the hotel's 16amp EVSE. Car would not connect and usual fixes failed. Drove to a 50kW charging station and tried DC but again no joy. (100% level set, no schedules.)

Back at the hotel the battery level was 11.5V. So I unpacked my Noco battery booster and connected it to the battery (with clicking (relay) noises coming from a unit to the right of the battery). The battery reached 14.2V and after I disconnected the booster went to 14.3V. I shut down the car and left it overnight during which time the battery went down to 12.5V.

This morning I powered up the car and it showed no faults and the expected 14.2V charging level. I connected it to the hotel's EVSE and it started charging with no issues.

I don't know if the fault would have corrected itself without the booster but I am just grateful to those posters who recommended carrying one.

Your voltage when the car is powered up seems to be on the low side and perhaps this is associated with a problem that is restricting power to the low power circuits leading to a drain from the 12V battery. We know that the car is supposed to keep the 12V battery topped up but this is the first time its action has been seen 'in the wild'.

Do you have a battery booster? Have you ever seen the battery voltage higher than 13.7V?

You could try disconnecting the battery, leaving it for 10 minutes then re-connecting to see if this 'hardware' reset works. See the Wiki on the actions required to be undertaken after a disconnect.

Hi and thanks for your reply. I don't have a battery booster and until today. the charge was often in the 14s. I haven't tried the disconnection yet, although when the battery was checked it would have been disconnected then.

 

[DoctorWolf]

Do you , or a neighbour/ friend have a Multimeter so you can keep an eye on the real battery voltage . It may be a problem with the 12 v charging system or how its just reported. Check the the battery terminals are clean and dry and the clamps are tightened up , for starters.

Cheers. I think I do have one so I can check. I'll look at the terminals although the mechanic didn't comment on any problems there when he checked the battery.