12 Volt battery going flat, no obvious reason.

[sguyj]

I have owned an MG4 X-Power for 2 years after previously owning an MG4 Trophy. In general I have been very pleased with both cars.
But I had a flat 12V battery recently for no apparent reason. I eventually managed to open the driver’s door with the manual key. But fiddly but ok. Everything dead as a DoDo of course.
I tried to trickle charge the 12V battery but after setting of the alarm, the trickle charger didn’t want to charge. So managed to jump start from my second car. Once started I left the car on for a while to get some charge into the battery. All ok now.
I don’t know what caused the battery to go flat. It was locked in my garage. It had not been used for about 5 days.
I suffered the exact same problem with my MG5S EV a month ago. Again no apparent reason for the 12V battery going flat. The MG5S is our daily car so it hadn’t been sat on my drive for days. On that occasion I successfully charged the battery with the trickle charger.
Has anyone suffered similar problems? Does anyone have any idea as to what may have caused the issues?
I’ve just bought a 7000 A Jump Start Power Pack Trekure to keep in the car in case this problem occurs again!

 

[Munnsy]

The factory fit battery is a cheapy standard lead acid, 45AH capacity.

In the application of it being used (a EV 12v auxillary powe source) 2 years lifespan is not a big surprise.

The problem is this type of battery does not like being kept at under 12.5 volts, which if you monitor the MG app when the car is parked up you will often see a resting voltage of 12.5-12.4v

This causes the plates of the battery to sulphate and reduce lifespan...

The answer is to replace battery with a higher quality brand (such as Yuasa) and/or higher capacity.

Another option on a EV, is to replace lead acid with a LIFEPO4 battery, expensive but should last many years.

 

[sguyj]

[
Thank you for your feedback Munnsy. Very useful.

 

[Chrisdriving]

I must be lucky, my 2016 Leaf still has original Renault/Nissan battery.

 

[Munnsy]

I must be lucky, my 2016 Leaf still has original Renault/Nissan battery.

Just depends on how the car maintains the charge of the battery. If it's not allowed to drop too low it will last long time.