How to balance MG5 EV 2021 pre facelift

[paulboy]

At 5 yrs and 40,000 miles my battery at recent service check was down to 85% is that about right? Also, how do I force a balancing charge. The car has never asked me to do one.

 

[Alb]

Charge to 100% on an AC Charger and leave it connected. You'll see it consuming a few hundred Watts whilst it balances before it switches off (this may take hours).
The manual says the car will tell you if it thinks it needs a balance but I've never heard of anyone actually seeing this.
Might be a good idea to get an OBD2 reader so you can see exactly what the cell voltage range actually is.

 

[SimonomiS]

Charge to 100% on an AC Charger and leave it connected. You'll see it consuming a few hundred Watts whilst it balances before it switches off (this may take hours).
The manual says the car will tell you if it thinks it needs a balance but I've never heard of anyone actually seeing this.
Might be a good idea to get an OBD2 reader so you can see exactly what the cell voltage range actually is.

I got this alert from the car (Mag5 pre FL) the other day for the first time ever after 85k miles! There was an audio alert (the same one as when starting when ready to select a gear) and a text message on the display that very rapidly disappeared along the lines of BMS balance charge required. I thought that I've done this many times but I'm on the IOG tariff which switches on & off remotely so perhaps doesn't let this happen. I'll do a granny charge overnight and see how that goes. The alert only seems to comes on when braking to a full stop

 

[paulboy]

Thank you both. Will try using granny charger overnight.

 

[kevin ellard]

At 5 yrs and 40,000 miles my battery at recent service check was down to 85% is that about right? Also, how do I force a balancing charge. The car has never asked me to do one.

As others have said, just leave it charging after it gets to 100% and it will balance itself. 85% seems suspiciously low though. I think that at 5 years old most people would expect it to still be over 90% unless badly treated.

 

[5teep]

My first MG5 pre fL was 98% on 45k miles at a bit over a year old. Charged every day on AC with small DC charges often. Maybe it's also an age thing? I don't know. Never worried about balancing, I just figured the car would take care of it.

 

[MickeySw]

At 5 yrs and 40,000 miles my battery at recent service check was down to 85% is that about right? Also, how do I force a balancing charge. The car has never asked me to do one.

85% seems low, however it would not be the first time that the wrong value was given.

An easy way to check SoH is to charge to 100% and reset trip data afterwards, the range should show WLTP - degradation..

 

[Jomarkh]

Thank you both. Will try using granny charger overnight.

It may take a few times to recover a bit of SOH percentage. Try and do it monthly.

 

[MickeySw]

It may take a few times to recover a bit of SOH percentage. Try an do it monthly.

Balancing alone won’t do much for SoH, you need to re-calibrate the BMS, I.e. discharge below 10% then AC charge without interruptions to 100% and let it plugged in until the car stops the process.

 

[decrep]

Balancing alone won’t do much for SoH,

I guess you mean reported state of health?????
calibrating the BMS shouldn't affect actual SOH

But balancing the cells should improve SOH but may not be fully reflected in reported SOH until BMS is calibrated.
Does that sound right???

 

[MickeySw]

I guess you mean reported state of health?????
calibrating the BMS shouldn't affect actual SOH

Agreed, reported SoH is usually calculated by the BMS based on a degradation formula which takes into account battery age, no of charge cycles, etc.

The MG5 manual recommends (although not very clear) to re-calibrate the BMS regularly (four times per year iirc).

By deep discharging/re-charging the BMS measures the current capacity of the HV battery. It then compares this value with the spec and determines the actual SoH.

If the values differ, reported SoH is corrected as for obvious reasons reported SoH should match actual SoH.

But balancing the cells should improve SOH but may not be fully reflected in reported SOH until BMS is calibrated.

Balancing will help preventing early degradation to make sure all cells work 'equally'. Yes, a well balanced HV battery has a higher capacity (vs a bad one) and therefore a higher SoH.

A BMS calibration will always include balancing for this very reason.

 

[Gomev]

..

The MG5 manual recommends (although not very clear) to re-calibrate the BMS regularly (four times per year iirc).

...

When I had mine I never found this info in the manual re calibration, I only found the info re equalisation charging. I have seen this same advice posted about the MG4 as well so is this something specific to MGs or just info that isn't widely known. If so why not ?

In my current car's manual there is nothing about equalisation let alone calibration. I suspect it balances during every charge as it's never out of balance whenever I check and I only charge to 100% before long journeys.

 

[MickeySw]

When I had mine I never found this info in the manual re calibration, I only found the info re equalisation charging.

You're correct, the following 'cryptic' entry is only in the MG5 FL manual:

"When using the vehicle on a daily basis, it is recommended to fully charge it at least once a week, which is conducive to the health maintenance of the high-voltage battery pack; every 3 months to half a year, a low-power (less than 10% or 1 grid) full charged is performed."

I have seen this same advice posted about the MG4 as well so is this something specific to MGs or just info that isn't widely known. If so why not ?

AFAIK every EV has some sort of (manual) BMS calibration function? Modern cells seem to be holding up very well when it comes to degradation and/or the algorithms are very accurate to predict it hence manual BMS calibration isn't really a big thing anymore...

In my current car's manual there is nothing about equalisation let alone calibration. I suspect it balances during every charge as it's never out of balance whenever I check and I only charge to 100% before long journeys.

The easiest way to verify balancing is to get the min/max cell voltage of the battery back via OBD.