ZS EV Mk2 51 kWh LFP battery - What is Your Voltage When Full?

[Peter WA]

Right after a full charge to 100%, when first turning on the car, what HV battery voltage do you get?

Please only reply if you have a 51 kWh LFP battery (standard range Mk2 ZS EV).

This is what I got this morning, 410V:

Background (TL/DR):
I am using OVMS to monitor my car. Doing that I noticed a very big difference in cell voltages when the battery gets full, and a lack of balancing to even out that discrepancy. I started discussing in this thread: ZS EV Mk2 51kWh LFP Battery - Not Balancing Massive Cell Deviation

Since hardly anyone has OVMS or an OBD2 dongle, that discussion is tough going. But every car owner can check the voltage on the car's screen after a full charge. Hence this new thread.

Back in 2020/2021 the Mk1 ZS EV had a software issue that, due to a lack of cell balancing, lead to severe degradation in range. Lots of discussion back then. For example this thread about the fixed software:

G

Thread 'BMS Update?'

Jun 12, 2021

Is it necessary to get the January BMS Update if my car did not get the bad one last year?
My dealer Eric Stead said that it was only needed if the car had the bad one to put it right
and that MG would tell them what updates the car was in need of. The car in question is
a ZS EV and was bought in March 2020. It has had the Comfort 2 update , the HV fuse change
and the replacement wiring loom in the door.

• ging353
• battery management system bms mg zs ev update
• Replies: 106
• Forum: MG ZS EV Forum

It is quite possible that the Mk2 ZE EV has a similar issue. One way to see whether that is the case across the board or only for a few cars, or possibly only my car, is to compare voltages when fully charged. The less balanced the cells are, the lower the voltage at the end of a full charge. Charging stops when the highest cell voltage hits 3.65V. With a big cell voltage deviation many cells will be much lower, adding up to a lower overall voltage of the battery pack.

Going by the experience from the Mk1, it took months for the issue to be acknowledged and more months for a software update to be developed and rolled out. Then it took many times of charging with the new software to get the affected battery packs back into balance.

 

[Grith]

Mine is much lower, 398, just getting it down to 10% so I can do a balance charge, hope this improves the voltage

Does anyone know what the minimum voltage should be, as you can see the car has only done 600+ miles, should I be getting in touch with the dealership? (This is my first EV)

 

[chowbenter]

400V on my gen ll ZSEV 2023 SR Trophy.

 

[fred12345]

If higher voltage like yours is to show anything, yours seems better than most others so nothing to worry about...

 

[Peter WA]

If higher voltage like yours is to show anything, yours seems better than most others so nothing to worry about...

Regarding your photos: the second one has load on the battery, 5A, that would have dropped the voltage. Also: surface charge will come off quite quickly. So really depends on how soon after the end of a 100% charge one looks.

As to worry: not sure that is the right conclusion, maybe I need to worry less than others, but maybe they should worry more.

I just checked my history records, unfortunately I lost data prior to last August. But back in September 2024 I still got 417V.

Edit: found an old backup file. Days after I got the car, in November 2022, the voltage peaked at 421.75V. July 2023 I still got 420.25V.

A well balanced pack (to the level I balance my home battery) would have the voltage peak above 426V. Basically: all cells at least 3.55V with just a couple of outliers that trigger a stop of charge at 3.65V.

Because the LFP voltage curve is so shallow people who only get 400V (assuming that really is immediately after a full charge, with no load) should notice a very significant reduction in range already. Maybe not shown by GOM, but certainly with an increased risk that one gets stuck when the lowest cell reaches the low voltage cut-off.

 

[SKA]

Sorry to hijack but I have a similar battery related question on the MK2 51kWh .....

I think mine (2022 model) is very poorly balanced (or the battery has degraded badly). I have had it since new so I know the consequences of winter and summer. But lately, the first 40% drops like mad , for example this morning I did a 40 mile trip and it dropped 40% and the gom still shows 4 miles per kWh. Meaning I would have used 10kwh which should be 20%.... That was when I left at 100% this morning.

My thought is that I have not charged it to 100% for long enough for balancing ? As I often will charge to 100% and may be leave for another 15 mins top prior setting off a long journey.

Does anyone know if I want to balance the cells by charging to 100%, how long do it leave it charging at 100% for? And will it stop by itself?

Thanks

 

[hmadsen]

My thought is that I have not charged it to 100% for long enough for balancing ? As I often will charge to 100% and may be leave for another 15 mins top prior setting off a long journey.

Does anyone know if I want to balance the cells by charging to 100%, how long do it leave it charging at 100% for,? And will it stop by itself?

Thanks

It will charge to 100% and then switch to the balancing and stop by itself when it is finished.

Depending on the wall "charger" you have it might be possible to see the actual current power draw. (If it has an app or something like that.)
Mine says 10kW when charging, but when it gets near 100% it will drop off and i think i have seen it as low as 500 watts when nearing the end of a balance cycle.

 

[SKA]

Thanks and presumably It will then reduce from 500 watts to 0 and completely stops once the balancing is completed? I may have to leave it for longer, As I only leave it be charged at 100% for maybe 30 minutes. Thanks all

 

[hmadsen]

Thanks and presumably It will then reduce from 500 watts to 0 and completely stops once the balancing is completed? I may have to leave it for longer, As I only leave it be charged at 100% for maybe 30 minutes. Thanks all

Yes it will stop when its good and ready

 

[Peter WA]

Thanks and presumably It will then reduce from 500 watts to 0 and completely stops once the balancing is completed? I may have to leave it for longer, As I only leave it be charged at 100% for maybe 30 minutes. Thanks all

And when you then start the car, have a look at the HV battery voltage on the display and let us know.

Also note: if the battery is very poorly balanced it might take multiple balancing sessions to get it back to normal.

If it actually does balance. I still have my doubts my car does. I can not find any evidence in the data I kept. It is entirely possible that a bug in the BMS software stops it from ever balancing.

 

[hermitdave]

402V for me. I have OBD2 plugged in but haven’t looked at any data yet

20k miles / 3 years old

 

[Grith]

Attempted a balance charge Thursday night, got car to 8% put it on a bump ChargePoint with Octopus at 11:00 (outside IOG range) as I wanted to override the 11:30-6:30 range and get a full charge. Following morning Octopus had terminated the charge at 6:30 with 91% in battery. Put it on charge again Friday night (Octopus app would not let me bump charge )
It is now showing 100% but I don’t know if balance charge achieved, anyone know if a break stops the balance procedure?
Now showing 401v which is slightly up from my previous 398v

 

[hermitdave]

Attempted a balance charge Thursday night, got car to 8% put it on a bump ChargePoint with Octopus at 11:00 (outside IOG range) as I wanted to override the 11:30-6:30 range and get a full charge. Following morning Octopus had terminated the charge at 6:30 with 91% in battery. Put it on charge again Friday night (Octopus app would not let me bump charge )
It is now showing 100% but I don’t know if balance charge achieved, anyone know if a break stops the balance procedure?
Now showing 401v which is slightly up from my previous 398vView attachment 35162

I would read at 100% . LFP is notorious with pack voltage

 

[Peter WA]

It is now showing 100% but I don’t know if balance charge achieved, anyone know if a break stops the balance procedure?

Assuming your car actually does a balance, a stop in between should not be a problem. It should balance every time it reaches 100%, if the cell voltage difference exceeds whatever threshold MG has programmed. Doesn't matter whether it came from 8% or 91%.

Quite likely it should even update SOH. The only time I had my SOH updated was a charge from below 20% to 100% with an interruption of half a day, but no driving in between.

 

[PerthPete]

I've charged my MG4 51 to 100% once since I bought it 2 months ago. There was no indication that any balancing was going on. Do LFP batteries do it or is it just the Li-ion?

 

[fred12345]

Assuming your car actually does a balance, a stop in between should not be a problem. It should balance every time it reaches 100%, if the cell voltage difference exceeds whatever threshold MG has programmed. Doesn't matter whether it came from 8% or 91%.

Quite likely it should even update SOH. The only time I had my SOH updated was a charge from below 20% to 100% with an interruption of half a day, but no driving in between.

From memory, can't remember where that was, for "best" balancing it was recommended to charge from about 10% to 100% and let it balance until it stops by itself. I normally do it from about 30% or so ...

 

[hmadsen]

I've charged my MG4 51 to 100% once since I bought it 2 months ago. There was no indication that any balancing was going on. Do LFP batteries do it or is it just the Li-ion?

The only "indication" is that the current it draws from the charger will go down.

My wall "charger" has an app and i can see how many amps it draws and when the car (Both EVs i own) nears 100% it will go down a lot, normally charging at 11kW but when it reaches 100% it drops to maybe 1kW in the end.

 

[hermitdave]

The inverter showing ZS balancing. Looks like 20 mins and it tails rapidly

Compare that to the home battery that has resistive balancing. Balance take far longer

 

[Outbackozzie]

My 2023 (delivered Mar24) MGZSSR charges to 415v. 96.9 SOH on EZS app.

 

[natasha y]

402V