MG5 won't balance charge (2020 pfl exclusive)

hastykev · Wednesday at 9:37 PM

emmrecs said:
No, or at least it certainly isn't for me. On one occasion I ran it down to below 5% and didn't experience any power limiting (just a realisation that I needed to be very gentle with my right foot!).

How old is your car and what mileage have you covered? Have you owned it from new? Mine is a 2022 PFL, approximately 18.5k miles, owned from new.

It's nearly 4 years with 72K miles. I'm the second owner. Thanks for the info

hastykev · Wednesday at 9:39 PM

MickeySw said:
It’s rare, but I have heard of MG5’s suffering from what appears to be a voltage imbalance caused by a weak cell.

I would start with a hard reset, I.e. disconnect the (-) pole of the 12V battery for a few minutes.

If that doesn’t make a difference, invest in a OBD dongle and check the cell voltages yourself or bring the car to the nearest dealer.

I shall try that tomorrow! I'm investing in the ODB dongle I've seen recommended here. I have two others, neither work with Car Scanner.

MickeySw · Wednesday at 10:37 PM

hastykev said:
I shall try that tomorrow!

Moving the steering wheel fully left & right should clear all the errors that will appear after re-connecting the 12V aux, otherwise driving a few yards should do the job..

Jomarkh · Thursday at 7:17 AM

hastykev said:
I shall try that tomorrow! I'm investing in the ODB dongle I've seen recommended here. I have two others, neither work with Car Scanner.

Hi, try Torquelite

Gomev · Thursday at 9:07 AM

hastykev said:
I shall try that tomorrow! I'm investing in the ODB dongle I've seen recommended here. I have two others, neither work with Car Scanner.

My PFL 5, and some others on here wouldn't work with any OBD, (they work with other cars) so be prepared that yours may be the same.
I would say that this is a dealer problem with the battery, I hope yours is a good one. What is the estimated range on the GOM when you charge to 100% and reset the accumulated trip and in normal mode ? This sounds similar to a problem that some early ZS EVs had.

AndyB87 · Thursday at 10:20 AM

hastykev said:
Hi. I have an MG5 Exclusive. I charge at home with an Easee charge. I always charge to 100% when I charge, yet the car complains almost all the time about needing a BMS balancing charge. Simply reversing from my drive causes the message to pop up. Also I have read here that some people can take their car down to 10% or less: I can't - I get the snail mode limiting power, even at 27% or higher? Is this in line with other people's experience?

I wasn't aware it had a snail mode. On a run back from Aberdaron I got home with 3% battery but the car was behaving normally, albeit slightly slower than when fully charged.

MickeySw · Thursday at 11:33 AM

AndyB87 said:
I wasn't aware it had a snail mode. On a run back from Aberdaron I got home with 3% battery but the car was behaving normally, albeit slightly slower than when fully charged.

‘Snail mode’ is a condition where the car limits the available power to prevent damage. A very common one is when a cell voltage drops below a safety limit which seems to be the issue here.

A functioning car will let you fully discharge the battery before snail mode is eventually activated.

emmrecs · Thursday at 3:33 PM

hastykev said:
It's nearly 4 years with 72K miles

That's high, IMO!!

Was it previously a taxi? If so, I wonder whether the first owner did not "take proper care" of it.

What warranty was it sold to you as having? If it has been a taxi I seem to recall that the warranty for such usage is pretty limited.

From what others have posted here, and my own experience, I think the advice to go talk to your dealer is what is definitely required.

crispyjay · Thursday at 4:20 PM

emmrecs said:
That's high, IMO!!

I should hit a little bit over 45k miles next month at 2 years old. Mostly commuting to office. Booked in for its 3rd service and garage wanted to MOT it - took some time to explain mileage does not equal years

I have found at lower end of battery % you don’t get full power if throttle is floored. More so under load uphill. But I’ve never experienced turtle mode.

hastykev · Thursday at 6:56 PM

MickeySw said:
Moving the steering wheel fully left & right should clear all the errors that will appear after re-connecting the 12V aux, otherwise driving a few yards should do the job..

Very cunning tip! I drove about and cleared the errors. Left the battery off for a good 20 mins.

Charged back to 100%. I'll let you know what happens.

hastykev · Thursday at 6:58 PM

emmrecs said:
That's high, IMO!!

Was it previously a taxi? If so, I wonder whether the first owner did not "take proper care" of it.

What warranty was it sold to you as having? If it has been a taxi I seem to recall that the warranty for such usage is pretty limited.

From what others have posted here, and my own experience, I think the advice to go talk to your dealer is what is definitely required.

Yeah, I think it was on airport runs. I met someone else with an MG5 doing just that too. The MG dealer did a battery SOH and it was 98%. Not too sure what to make of that! However, clearly snail mode at 27% is off.

MickeySw · Thursday at 11:04 PM

hastykev said:
Yeah, I think it was on airport runs. I met someone else with an MG5 doing just that too. The MG dealer did a battery SOH and it was 98%. Not too sure what to make of that! However, clearly snail mode at 27% is off.

If yours is a long range model, then a reported SoH of 98% seems (given the age and mileage) excellent as in ‘too good to be true’.

If it’s a standard range, it could be more realistic if it has one of these rumoured ‘reject LR battery’ fitted.

The ‘tortoise mode’ could be caused by either a weak cell or faulty voltage reporting circuit; a repair will most likely require removing and opening the HV pack or replacing it altogether.

I can think of a 3rd (very unlikely) cause: the car vastly overestimates the actual capacity (SoH) I.e. the battery is essentially empty but still shows a SoC of 27%.
This would effectively mean the actual SoH is in the 70-80% range?

hastykev · Friday at 5:39 PM

MickeySw said:
If yours is a long range model, then a reported SoH of 98% seems (given the age and mileage) excellent as in ‘too good to be true’.

If it’s a standard range, it could be more realistic if it has one of these rumoured ‘reject LR battery’ fitted.

The ‘tortoise mode’ could be caused by either a weak cell or faulty voltage reporting circuit; a repair will most likely require removing and opening the HV pack or replacing it altogether.

I can think of a 3rd (very unlikely) cause: the car vastly overestimates the actual capacity (SoH) I.e. the battery is essentially empty but still shows a SoC of 27%.
This would effectively mean the actual SoH is in the 70-80% range?

Thanks for your detailed reply.

I just downloaded the log of the last charge. Car was at 100% anyway. This looks to me a lot like a balancing charge (at last!)

Will see what happens. The last service printout from the dealer said 98%. Will keep you posted!

MickeySw · 2025-04-12T07:51:35+0100

hastykev said:
. This looks to me a lot like a balancing charge (at last!)

It looks like the car successfully balances the cells in an hour and a bit.

Can you confirm that all looks good when you turn on the car, e.g. the message only pops up when reversing?

This could indicate that (at least) one cell’s voltage drops significantly under load (car moving) and eventually goes below the limit around 30% SoC?

MG5 won't balance charge (2020 pfl exclusive)

hastykev

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