12V battery (theres many of these!)

[buln]

Hi guys,

Seen a few posts about 12V batteries... I've had issues since delivery. 12V died so was rescued AA, however jumping it didn't work. As a result they recovered to a garage, they replaced the 12V and sent me on my way.

Called AA again last week as was dead on drive... they jumped and all good. I did a long journey yesterday (approx 200mi round trip) so thought that's plenty to fully charge the 12V. I keep having issues though with the warning 12V low.

When I observed, I noticed a reading of 14.3V when in ready. Drops to 12.8V when not in ready mode and drops exactly 0.1V per second, right down to 9.1V (literally in half a min) where I then went back into ready mode in fear I was going to lose power again.

Dealership says they've already replaced and the volt readings in car are probably just wrong but not to worry - I assume it's something else with the 12V already being replaced?

 

[Alb]

Dealership says they've already replaced and the volt readings in car are probably just wrong but not to worry

They are talking complete nonsense.

 

[Gadget Geek]

Sounds like they've given you a secondhand battery out of the workshop.

14.3V is measuring the supply from the traction battery. 12.8V is the actual battery voltage, and that should remain constant for more than a few minutes! The battery needs a test under load to see if it is holding its charge.

 

[buln]

Thanks... After the 9.1V I'm now on the drive attempting to turn the car off with no luck.

Looks like I need another jump!

 

[pollenface]

Time for a new 12v battery

 

[alekc]

Hijacking the thread a bit: what battery is recommended? Tayna suggests AGM type, but given the cost I would be tempted to go with classic lead acid since we don't need to crank anything in the car. Opinions?

 

[Coulomb]

I would be tempted to go with classic lead acid since we don't need to crank anything in the car.

The suggestion for AGM (which is a form of lead acid battery) is not for high currents, although it helps to be able to absorb the over 100 A of [i[charging[/i] current that the DC-DC can provide. It's more to be able to last well with the lack of charging opportunity. At least, that's how it is for the Nissan Leaf, which does recharge the auxiliary battery when parked, but often doesn't charge for long enough. AGM batteries can absorb more charge in that short recharge window.

But I'm wondering if the MG ever charges the auxiliary battery when parked. I've certainly never noticed my Mark 1 doing it, and I notice my Leaf doing it every few days.

 

[Pebble]

Look for a non-starter battery, aka "leisure" battery, maybe the Banner Bull for example. Designed for multiple discharge cycles where cranking current isn't required.

 

[alekc]

But I'm wondering if the MG ever charges the auxiliary battery when parked.

I am waiting for Bluetooth monitor to arrive, hopefully will be able to see the answer to that question. Given that I've parked my car for 11 days and it went completely flat it would seem that no, at least not always (although it was low on main battery, so that could have played a role)

 

[JCFlippen]

Hijacking the thread a bit: what battery is recommended? Tayna suggests AGM type, but given the cost I would be tempted to go with classic lead acid since we don't need to crank anything in the car. Opinions?

Just go for a Bosch 52 ampere battery with 4 year warranty About £107.

 

[Rayz]

Hijacking the thread a bit: what battery is recommended? Tayna suggests AGM type, but given the cost I would be tempted to go with classic lead acid since we don't need to crank anything in the car. Opinions?

Just go for a Bosch 52 ampere battery with 4 year warranty About £107.

I was told same Tanya 027 AGM by MG Dealership Service Dept it cost £125 and battery is a lot better voltage wise and not drawing as much power from DC-DC Rectifier, noticed the blue display is keeping around 14v, and getting up to better reading on cold days for instance 3.8- 4 Miles per KWH on 7-12 c .On my 2022 MG5 EV LR. This wasn't a one off test. I also parked car up for up to ten days and only lost 25% of full battery charge. I've got a BM2 Monitor which in my opinion is brilliant.

 

[Roldorf]

I have the comfort version. Parked for over six weeks no loss on battery. I think the battery losses could have something to do with the trophy version Wi-Fi and connectivity issues.

 

[pollenface]

There are EV purposed 12v batteries, I'd go with one of those

 

[Rayz]

The BM 2 Monitor is good . With having the BM2 I found the only time the MG5 LR 12v Battery charges from the dc-dc rectifier is when the car is in the Ready position either parked up or Driving .