BMS (Battery Management System) updates
We are in communication with MG about the BMS update situation and it has caused major problems for quite a few drivers - we are trying to determine exactly how many from MG. The October BMS update (1016620R040) was faulty and led to slow equalisation charging, lower range and increased battery drain. They have confirmed several times that if owners cars are on the VIN list of those who have had the faulty update installed in error between late October and mid January, there should be ZERO charge to install the latest fix version. The latest BMS update (1230621A01) issued end January 2021 has solved the problem - but your battery will take a while to return to top condition. (We understand this could be up to 30 equalisation charges.) Contact your dealer to have it installed. If your car was affected, you will also be offered a free service. See posts below for useful information and advice. If you are a new purchaser, check with your dealer whether the newest BMS update is installed before you take delivery.
Comment from Miles Roberts (Chorley - recommended dealer) 11/2/21
BMS voltages
MG has made some adjustments to the ZS EV battery pack voltage limits to increase pack longevity, but maintain the range. This is part of the new January BMS update. The new maximum voltage will be around 449/450V (assuming no loads on like climate etc). The minimum voltages have been adjusted to keep the range equal. This may also allow the car to have better regeneration from 100% charge. After the BMS update it is worth resetting both the trip meters to zero and the range will be recovered back to full capacity reading. Owners will no longer see the previous low range numbers.
Helpful advice from Chris Wiggins (experienced EV driver and ZSEV owner) 10/2/21
BMS Balancing - ZSEV (Not MG5 issue)
This is specifically written to hopefully answer some questions about balance charging regarding those of us who had the dodgy version of software deployed to only the ZS EV between 24th Oct and early Jan, and much of the stuff in here only relates to those people when they have the fixed version on their cars, but might be of general interest to others.
Some of the info is about balance charging generally, other is based on what I have deduced using OVMS, which gives a more in depth report back on the battery, than is available otherwise. I can see the voltage of the lowest and highest cells in each pack, plus the overall battery voltage with greater accuracy. Some may be conjecture, but I’ll try to be clear about what I am confident about, what I am suggesting based on the evidence, and what I am guessing at.
What is balance charging and why do I need it?
All electric cars from all companies need balance charging. The ZS car battery is made up of 100's of cells (108 across 9 banks in the MG if I recall correctly), each individual cell (think of a cell as an individual household AA battery) holds a charge of around 4.2v when fully charged. When you charge or use a car, power is taken from the cells. In an ideal world that happens totally uniformly across the 108 cells, but in the real world some cells charge slightly quicker some slower, some drain quicker, others slower. So you end up with a mismatch in voltage between the cells. This effect is magnified by rapid charging.
A "balance charge" happens automatically at the end of any type 2 charge. (ie granny or 7kw home /destination charger). If a battery is in good health, it might be an hour or 2 of essentially shuffling little bits of power between cells to balance them all out. When the MG logo is lit solidly rather than pulsing on and off, it is balancing.
What appeared to happen with the faulty version is that process wasn’t working correctly, and cells were becoming more out of balance with each other – the car recognises this and when it is bad enough tells you with a message on the dash to say “Please slow charge”. This message will continue to pop up occasionally after the fix has been applied until you are back to normal, as it’s a separate bit of code that essentially looks and sees imbalance, and then informs you.
The side effect is when you charge to “full” some of the cells will be full, some will be slightly empty and some will be more empty. This leads to less power in the overall battery, (and therefore the lower voltage we can see). The fix version has multiple tasks it needs to achieve, it needs to try to balance all the "out of balance" cells, plus deal with the natural new day to day forces trying to further unbalance the cells, plus it is wanting to balance the banks between each other.
Charging fills the battery until cells say they are full, and then starts the micro shuffling of power. This takes a while, and it has a finite amount of time to achieve it. This is for two reasons. Both because it is capped at about 11 hours after the charging finishes, and also because people get in and want to drive the car in the morning. So for example, if your charge window is from midnight, it might finish filling the car by 4am, if you drive at 8am, it only has a 4 hour window to balance, this is normally plenty of time, but with the added issue of catching itself up means it takes more charge occasions to do it.
The indicated range is not a good indication of success or failure of the balance, it is being messed around by the inconsistent battery, plus temperature and a host of other factors so is not useful in any diagnosis around this.
What I have learned
Your first charge after the fix, will likely give you, in percentage terms, the biggest one day increase. That’s the low hanging fruit and it is likely to be smaller bites after that. Using the balance, unplug, replug and re-balance approach, it will try to spend another hour or so balancing, the measured effect is miniscule on the battery, and in my view it isn’t significantly beneficial.
I haven’t yet got enough data to back this next statement up, but my belief is a deeper discharge and recharge will result in a greater improvement than discharging to say 80% and recharging. But as I said, I can't prove that with evidence yet, so I might be wrong.
The way that a 11 hour balance shuffles things around and moves the highest cells downward slightly, and the lowest cells upward, does sometimes mean you see zero improvement in voltage at the end. However, I can see in the OVMS data that it's still been successfully balancing, and narrowing that gap between good and bad cells, resulting in typically every other night or perhaps 1 night in 3, the voltage will improve. The voltage (whilst its all you can really go on without OVMS) isn’t actually a good measure of balance but it is a symptom of where your battery is.
I haven’t yet proven this, but it shouldn’t matter if you balance with a 3kw granny or a 7kw home charge point as the balance happens at a much much lower current at the end. The only difference might be the actual charge time will take longer on the granny, so if you are driving away early the next morning, the balance time will be less. Charging for 4 hours and only allowing 4 hours to balance will help, but much of the significantly beneficial balancing happens in the latter stages.
The longer you can leave the car charging (and therefore balancing after charging) the better. I know it sometimes seems fruitless, but I can see clear improvements in the underlying data even on days that the overall voltage doesn’t improve.
My conclusion
Yes (for my car at least) I think the new version has fixed the problem, and yes it will also take a while, and multiple equalisation charges to fully fix the battery.
Comment from Miles Roberts (Chorley - recommended dealer) 11/2/21
BMS voltages
MG has made some adjustments to the ZS EV battery pack voltage limits to increase pack longevity, but maintain the range. This is part of the new January BMS update. The new maximum voltage will be around 449/450V (assuming no loads on like climate etc). The minimum voltages have been adjusted to keep the range equal. This may also allow the car to have better regeneration from 100% charge. After the BMS update it is worth resetting both the trip meters to zero and the range will be recovered back to full capacity reading. Owners will no longer see the previous low range numbers.
Helpful advice from Chris Wiggins (experienced EV driver and ZSEV owner) 10/2/21
BMS Balancing - ZSEV (Not MG5 issue)
This is specifically written to hopefully answer some questions about balance charging regarding those of us who had the dodgy version of software deployed to only the ZS EV between 24th Oct and early Jan, and much of the stuff in here only relates to those people when they have the fixed version on their cars, but might be of general interest to others.
Some of the info is about balance charging generally, other is based on what I have deduced using OVMS, which gives a more in depth report back on the battery, than is available otherwise. I can see the voltage of the lowest and highest cells in each pack, plus the overall battery voltage with greater accuracy. Some may be conjecture, but I’ll try to be clear about what I am confident about, what I am suggesting based on the evidence, and what I am guessing at.
What is balance charging and why do I need it?
All electric cars from all companies need balance charging. The ZS car battery is made up of 100's of cells (108 across 9 banks in the MG if I recall correctly), each individual cell (think of a cell as an individual household AA battery) holds a charge of around 4.2v when fully charged. When you charge or use a car, power is taken from the cells. In an ideal world that happens totally uniformly across the 108 cells, but in the real world some cells charge slightly quicker some slower, some drain quicker, others slower. So you end up with a mismatch in voltage between the cells. This effect is magnified by rapid charging.
A "balance charge" happens automatically at the end of any type 2 charge. (ie granny or 7kw home /destination charger). If a battery is in good health, it might be an hour or 2 of essentially shuffling little bits of power between cells to balance them all out. When the MG logo is lit solidly rather than pulsing on and off, it is balancing.
What appeared to happen with the faulty version is that process wasn’t working correctly, and cells were becoming more out of balance with each other – the car recognises this and when it is bad enough tells you with a message on the dash to say “Please slow charge”. This message will continue to pop up occasionally after the fix has been applied until you are back to normal, as it’s a separate bit of code that essentially looks and sees imbalance, and then informs you.
The side effect is when you charge to “full” some of the cells will be full, some will be slightly empty and some will be more empty. This leads to less power in the overall battery, (and therefore the lower voltage we can see). The fix version has multiple tasks it needs to achieve, it needs to try to balance all the "out of balance" cells, plus deal with the natural new day to day forces trying to further unbalance the cells, plus it is wanting to balance the banks between each other.
Charging fills the battery until cells say they are full, and then starts the micro shuffling of power. This takes a while, and it has a finite amount of time to achieve it. This is for two reasons. Both because it is capped at about 11 hours after the charging finishes, and also because people get in and want to drive the car in the morning. So for example, if your charge window is from midnight, it might finish filling the car by 4am, if you drive at 8am, it only has a 4 hour window to balance, this is normally plenty of time, but with the added issue of catching itself up means it takes more charge occasions to do it.
The indicated range is not a good indication of success or failure of the balance, it is being messed around by the inconsistent battery, plus temperature and a host of other factors so is not useful in any diagnosis around this.
What I have learned
Your first charge after the fix, will likely give you, in percentage terms, the biggest one day increase. That’s the low hanging fruit and it is likely to be smaller bites after that. Using the balance, unplug, replug and re-balance approach, it will try to spend another hour or so balancing, the measured effect is miniscule on the battery, and in my view it isn’t significantly beneficial.
I haven’t yet got enough data to back this next statement up, but my belief is a deeper discharge and recharge will result in a greater improvement than discharging to say 80% and recharging. But as I said, I can't prove that with evidence yet, so I might be wrong.
The way that a 11 hour balance shuffles things around and moves the highest cells downward slightly, and the lowest cells upward, does sometimes mean you see zero improvement in voltage at the end. However, I can see in the OVMS data that it's still been successfully balancing, and narrowing that gap between good and bad cells, resulting in typically every other night or perhaps 1 night in 3, the voltage will improve. The voltage (whilst its all you can really go on without OVMS) isn’t actually a good measure of balance but it is a symptom of where your battery is.
I haven’t yet proven this, but it shouldn’t matter if you balance with a 3kw granny or a 7kw home charge point as the balance happens at a much much lower current at the end. The only difference might be the actual charge time will take longer on the granny, so if you are driving away early the next morning, the balance time will be less. Charging for 4 hours and only allowing 4 hours to balance will help, but much of the significantly beneficial balancing happens in the latter stages.
The longer you can leave the car charging (and therefore balancing after charging) the better. I know it sometimes seems fruitless, but I can see clear improvements in the underlying data even on days that the overall voltage doesn’t improve.
My conclusion
Yes (for my car at least) I think the new version has fixed the problem, and yes it will also take a while, and multiple equalisation charges to fully fix the battery.
Comfort 2 update - info from MG website
( NB - if you purchased your car after mid June 2020, the car should have had the Comfort 2 update installed and therefore bongs etc dealt with. If you are being asked to pay for this update in 2021 as a new purchaser, you should definitely query this.)
During the lifespan of a vehicle model, various changes can be made to interior trim, exterior cosmetics or system functions to ensure that it features cutting edge technology and remains attractive to potential buyers. MG ZS EV models manufactured after mid-June 2020, will have a newly developed 2nd generation of Comfort System Operation installed on the car. This is now available for customers who wish to benefit from these later updates on earlier build models.
Whilst all the below features involve software changes to key components on your vehicle, the updated software is not available to cars with 1st Generation software as a ‘warranty upgrade’. MG’s warranty is there to cover the cost of repair or replacement of a failed part due to a manufacturing defect, and not for updates/upgrades, and will therefore be chargeable. Please speak to your MG dealer to find out associated charges for this update.
This new 2nd generation of Comfort System Operation includes changes to:
During the lifespan of a vehicle model, various changes can be made to interior trim, exterior cosmetics or system functions to ensure that it features cutting edge technology and remains attractive to potential buyers. MG ZS EV models manufactured after mid-June 2020, will have a newly developed 2nd generation of Comfort System Operation installed on the car. This is now available for customers who wish to benefit from these later updates on earlier build models.
Whilst all the below features involve software changes to key components on your vehicle, the updated software is not available to cars with 1st Generation software as a ‘warranty upgrade’. MG’s warranty is there to cover the cost of repair or replacement of a failed part due to a manufacturing defect, and not for updates/upgrades, and will therefore be chargeable. Please speak to your MG dealer to find out associated charges for this update.
This new 2nd generation of Comfort System Operation includes changes to:
- Faster system self-check when powering ‘ON’
- Infotainment volume maintains and restarts at previous volume setting after powering ON/OFF
- Auto High Beam system disable option available in menu settings
- General warning chime quality improvements and reduced volume
- Warning chimes reduced for MG Pilot and Key Reminder
- Vehicle temperature and temperature alarm featured in the instrument display
- Vehicle range always on display in instrument pack
- Vehicle can be unlocked during A/C charging, when re-locked charging automatically resumes