12v Battery Charge low may be limited start vehicle (AMENDEED VOLTAGE READINGS)

[Tom Hartley]

12V BATTERY CHARGE LOW MAY BE LIMITED. PLEASE START VEHICLE.

We have owned our MGZSEV Exclusive from new, it will be 6 in September.

During May/June 2025 the above dashboard warning appeared and after seeking advice from the EV community I replaced the 12v battery (I retained the original....too long a story but there was nothing wrong with it ).

Recently the above warning has reappeared, as too when I have refitted and tried out the old one).

Both batteries mentioned have been charged with a Blink recommended 6A battery charger and checked on and off the EV with an amp meter.

The new battery after a run, engine off, car locked read 12.74, when disconnected, left to stand it read 16.47 / 6 .... differs slightly during various repeat tests.

Those tests have been carried out during different weather temperatures, the last being today when it was unbelievably a sunny 11 degrees outside.

I also left it disconnected as allegedly the EV can then lose any ghost glitches.

Today after a 10 mile round journey. I alighted from the EV, locked it, opened the boot to unload shopping for a few minutes and then closed the boot, the warning appeared.

I previously removed the boot light bulb to eliminate any potential battery drain source

The EV has its full MG dealer service history, the last being September 2025..

I have not yet booked the EV in for an investigation as in the area the "dealers" seemingly want it for the day to examine any warranty work and then a revisit for any potential fix should something be identified. I am hoping to avoid wasted trips.

Has anyone else experienced the warning under the circumstances outlined, if so has a remedy been found?

Apologies for the long story.

 

[Tim Green]

Tom, I remember your story about needing a new battery about a year ago. Our car is an early 2020 so is now over 6 years old. Recently I noticed the sometimes the car would not "start" but acted like I had not put my foot on the brake. Also I noticed that the 12v battery was low, showing under 12v when the car was not running. Also I started getting the "13v warning" that you had.. I replaced the 12v battery and all is fine again.
I do not know what you mean about the battery reading 16.47v? I think that is impossible from a 12v battery. If fully charged they should read about 13v or 13.5 v with no load. If it is really reading 16v there must be something wrong with it.

 

[gonzo]

Where did you read the ~16V ?? Was that indicated on the vehicle or an a separate voltmeter?
(You mention using an amp meter. Not sure if you were measuring charge current or actually meant a voltmeter/multimeter?)
If using an external voltmeter, where did you take the measurements across??
Is your meter reading correctly?

I have seen odd voltage readings where there is poor earthing. On an ICE vehicle, this tends to prevent cranking. On an EV, it may not show up so obviously. Just results in there being a few volts loss, enough to cause problems/warnings, on the car systems. And an apparent excess voltage increase when charging.

 

[Pete G]

Our ZS EV had the same message come up when we were in town shopping. We drove to a battery shop and had them test the 12 volt battery. The battery passed the load test.
Still I got them to put in a new battery anyway.
No more messages from the car about the 12 volt battery being low.
In your situation I suggest cleaning the battery terminals and lugs and see if that helps.
Also make sure the earth connection on the car is clean as well.
Our battery had a small hole in one corner at the top, that a rat had chewed into it. That is one reason I did not trust it and had it changed.
good luck
Pete

 

[Tom Hartley]

Tom, I remember your story about needing a new battery about a year ago. Our car is an early 2020 so is now over 6 years old. Recently I noticed the sometimes the car would not "start" but acted like I had not put my foot on the brake. Also I noticed that the 12v battery was low, showing under 12v when the car was not running. Also I started getting the "13v warning" that you had.. I replaced the 12v battery and all is fine again.
I do not know what you mean about the battery reading 16.47v? I think that is impossible from a 12v battery. If fully charged they should read about 13v or 13.5 v with no load. If it is really reading 16v there must be something wrong with it.

Apologies for my mistyped voltmeter readings the information should have read:

The new battery after a run, engine off, car locked read 12.74, when disconnected, left to stand it read 1227 / 6 .... differs slightly during various repeat tests.
I have also retested my now spare old battery and it too shows a drop of .4 to .5 drop when subjected to the same tests.
I have examined visible wiring and terminals were and are clean and leads were secure.
Anyone any ideas / remedy