Low Battery - Reduced Power

[DriverInNorway]

I have done something very similar and written a templated letter to the dealership here in Norway. The consumer rights in Norway are nearly identical and so within the first 30 days, for a significant and/or dangerous fault, you can simply return the car. After 30 days, the retailer has one chance to repair it. There are templated letters for this.

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Mine is over the 30 days. But, I am not accepting the car back if it involves me having to recharge it a number of times before it has its advertised range, so I will ask for a new battery if that is the case and they can recondition the old one. I love the car too but if a new ICE car developed a fault like this, it would be recalled as it is dangerous.

 

[Mike]

Interesting and wonder if this could be a common problem, post update, which if you charge daily and don't let the SOC go below 40% you would never notice this...

I had power limited today. I was around 30% SoC and limited to 60/70%. It was about 1-2°C st the time.

I had it a lot with the duff BMS.

 

[Mike]

I've emailed the dealer I brought the car from today, it's 14days on Tuesday since purchase.

I've mentioned
"I would expect the car to be able to do 163miles as per the WLTP test in a fully usable state, if part of this 163 mile range is with a severely restricted car that cannot maintain the necessary safe road speed, then it does not have the advertised usable 163mile WLTP range."

Will see what happens, hopefully there's a fault that can be fixed!
We love the car and want to keep it if we can.

163 miles in cold wet weather?

The normal for me at the time of year is 100-120 miles. I would never expect more than that range in winter.

Just like an ice will never give best economy in winter or ever match its WTLP figures.

 

[DriverInNorway]

It is not just the range that is an issue. Yes, a drop in range due to a drop in temperature is expected. But the power reduction to 40% for a large percentage of the reduced range is not acceptable. There is not even a warning that power is reduced, just a failure for the car to deliver power greater than 40% which actually drops to 20% without warning when my reported range is around 90km. Anyway, I will update this forum with the results from the dealer. They have to have a fair chance to fix it once.

 

[WAC 768]

I had power limited today. I was around 30% SoC and limited to 60/70%. It was about 1-2°C st the time.

I had it a lot with the duff BMS.

I know you've had this before and also the new BMS update, so it looking like they've fixed one problem but not the power reduction..

 

[JodyS21]

I have done something very similar and written a templated letter to the dealership here in Norway. The consumer rights in Norway are nearly identical and so within the first 30 days, for a significant and/or dangerous fault, you can simply return the car. After 30 days, the retailer has one chance to repair it. There are templated letters for this.

How to reject a car: the Consumer Rights Act 2015 | Carbuyer

What is the Consumer Rights Act 2015, and how can it protect you if something goes wrong when buying a new car? Here’s everything you need to know

www.carbuyer.co.uk

Mine is over the 30 days. But, I am not accepting the car back if it involves me having to recharge it a number of times before it has its advertised range, so I will ask for a new battery if that is the case and they can recondition the old one. I love the car too but if a new ICE car developed a fault like this, it would be recalled as it is dangerous.

Thank you for that, it's going to be VERY useful for me.

One VERY interesting and pertinent line
"Fit for purpose: the car must perform as you’d expect; it should have enough power to go up steep hills"

 

[Jasonmgev]

Mine does the same. It is 3 months old and has not had any software upates yet. When I come to any sort of hill and I have around a third of the battery capacity left, power is reduced and the maxiumum speed I can get is 50 kmh which in a 70 kmh zone is not particularly enjoyable. The temperate is -19 C but this should not affect the car to that extent. The range is also severely reduced in this temperature. The GOM shows 191 km after a full over night charge, and after 10 minutes of heating the car before leaving and driving 23km to work it is down to aroung 100km. Less than 10km later power is reduced and as it is up hill for two thirds of the way home, it is a slow crawl and I have to turn off the heater. By them time I get home, it is down to around 50km range but this range is largely unusable as it is power limited by then. So at the moment in around -19 C, I have a usable range of about 30km. Off to see the dealer this week to see what they say.

exact same issue.. car is now sitting at the dealer and got a rental car, while they try figure it out.. Got called today to say that they are waiting for MG to get back to them, as they cant figure it out locally

 

[DriverInNorway]

OK, so I sent the templated letter to the car dealership and then dropped the car off with them. After some time, they confirmed the car was delivered with BMS update software that has this bug in it. The rectification is to update the software and recondition the battery. This can take up to a month depending on how imbalanced the cells are. They will perform this reconditioning at their premises. In the meantime I have a Tesla hire car paid for by them. So far, I am pleased with the dealership's response. I am not particularly pleased with MG for delivering a car and not doing a recall of the car much sooner. it has been difficult to realise there was a problem with the car as the temperature drop here has coincided with the drop in range. However, the lack of power was a clear sign that something was not right.

 

[DriverInNorway]

exact same issue.. car is now sitting at the dealer and got a rental car, while they try figure it out.. Got called today to say that they are waiting for MG to get back to them, as they cant figure it out locally

Mine was delivered in November 2020 and the dealer stated it has been delivered with BMS software that has since been discovered to have a bug. Maybe it would be useful to inform your dealer of this but I imagine MG are well aware of which cars have been delivered with this incorrect software. Hope it gets resolved for you.

 

[DriverInNorway]

Thank you for that, it's going to be VERY useful for me.

One VERY interesting and pertinent line
"Fit for purpose: the car must perform as you’d expect; it should have enough power to go up steep hills"

Yes, precisely. that is what I used as a direct quotation when stating the car did not meet the quality expected. Rather than just giving the car back to the dealer to repair, the templated letter really seemed to jolt them into proper remedial action. I guess MG and or the dealers do not want cars to be returned to them and a refund demanded which is the next step for a new car with a significant fault under 6 months old. Glad it was also of use to you.

 

[JodyS21]

OK, so I sent the templated letter to the car dealership and then dropped the car off with them. After some time, they confirmed the car was delivered with BMS update software that has this bug in it. The rectification is to update the software and recondition the battery. This can take up to a month depending on how imbalanced the cells are. They will perform this reconditioning at their premises. In the meantime I have a Tesla hire car paid for by them. So far, I am pleased with the dealership's response. I am not particularly pleased with MG for delivering a car and not doing a recall of the car much sooner. it has been difficult to realise there was a problem with the car as the temperature drop here has coincided with the drop in range. However, the lack of power was a clear sign that something was not right.

I am very happy to hear this
That is a great outcome. Cannot fault that dealers response.
As much as it is exactly what they should do given the issue, I very much doubt many other dealers would do this...

 

[Mike]

I am very happy to hear this
That is a great outcome. Cannot fault that dealers response.
As much as it is exactly what they should do given the issue, I very much doubt many other dealers would do this...

Not in the UK unless it’s exceptional circumstances.

 

[WAC 768]

Update, I have finally managed to get out and run the battery down following the second update of my Jan BMS and can confirm the problem with the reduced power is still there; however, not as severe. My assumption is the reduction is very much temperature dependent, given the results below (Note: This is from a speed > 15MPH not a standing start and balanced battery 450v) .

Power Output @ circ 40 miles (0C = 60% -> 11C = 70%)

Power Output @ circ 16 miles on an incline (0C = 30% -> 11C = 40%)

Either way this is unacceptable and let's see what the dealer / MG say...

 

[JodyS21]

Update, I have finally managed to get out and run the battery down following the second update of my Jan BMS and can confirm the problem with the reduced power is still there; however, not as severe. My assumption is the reduction is very much temperature dependent, given the results below.

Power Output @ circ 40 miles (0C = 60% -> 11C = 70%)

Power Output @ circ 16 miles on an incline (0C = 30% -> 11C = 40%)

Either way this is unacceptable and let's see what the dealer / MG say...

Yes that's not what I got in my test on Monday.

To clarify, I stopped then foot flat to floor, that's when I eventually saw a power reduction. It went to 80% but then dropped quite quickly.
So nowhere near as bad as what you're experiencing.

I did read something yesterday about peak and continuous power spec of the motor. I wonder if that's partly why it always seems to drop after first hitting around 100% in normal conditions i.e. the motor cannot handle much of a sustained 100% power.

 

[DriverInNorway]

Yes that's not what I got in my test on Monday.

To clarify, I stopped then foot flat to floor, that's when I eventually saw a power reduction. It went to 80% but then dropped quite quickly.
So nowhere near as bad as what you're experiencing.

I did read something yesterday about peak and continuous power spec of the motor. I wonder if that's partly why it always seems to drop after first hitting around 100% in normal conditions i.e. the motor cannot handle much of a sustained 100% power.

When I get my car back, which may not be for a few weeks. I will ask to test drive it with one of the workshop staff and see what it does. The car should be able to deliver most of its power throughout I guess 90% of the battery capacity. I can understand it dropping to conserve range in say the final 10% once it issue a warning that it is doing so.
Under normal driving conditions this power drop is probably not noticeable, it will only be under heavy acceleration, when you need the power to overtake safely, or when going up hill. I will see if I can find anything about power delivery in other electric vehicles. It might be common across EV vehicles. I doubt it is, but worth a bit of research.

 

[WAC 768]

When I get my car back, which may not be for a few weeks. I will ask to test drive it with one of the workshop staff and see what it does. The car should be able to deliver most of its power throughout I guess 90% of the battery capacity. I can understand it dropping to conserve range in say the final 10% once it issue a warning that it is doing so.
Under normal driving conditions this power drop is probably not noticeable, it will only be under heavy acceleration, when you need the power to overtake safely, or when going up hill. I will see if I can find anything about power delivery in other electric vehicles. It might be common across EV vehicles. I doubt it is, but worth a bit of research.

Keep us posted and I would expect 100% of the power to be available until such a time you get a reduced power warning that could be like you say within the last 10%

 

[DriverInNorway]

Keep us posted and I would expect 100% of the power to be available until such a time you get a reduced power warning that could be like you say within the last 10%

So, I have been doing some research on constant voltage delivery of batteries. If there are any battery or electrical experts here, feel free to comment or correct. So, the individual cells that make up the battery pack have a minimum and maximum voltage range over which they should be discharged down to and charged up to. The cells are not all perfect so some will discharge and charge at slightly different rates. One of the jobs of the Battery Management System is to control this charging and discharging and balancing. The BMS is most likely designed to never discharge a battery beyond its minimum. Therefore it has to provide constant voltage by 'borrowing' from other cells once some cells approach their minimum. An bad BMS algorithm would result in a badly imbalanced battery. There will be so many cells that are at, or near their minimum voltage that there wont be enough cells for the BMS to provide the constant voltage and we will see voltage sag. Combine this with the lower ranges due to the cold weather and this effect happens very soon in the discharge cycle of the battery. So, it is more important to have a fully balanced battery in cold temperatures so that the BMS can provide a constant voltage for the longest time from a set of near equal cells. So, even after the new BMS algorithm is applied, it will take many charge/discharge cycles to correctly balance all the cells, so until that time, the voltage sag will happen early in the discharge cycle.

 

[WAC 768]

So, I have been doing some research on constant voltage delivery of batteries. If there are any battery or electrical experts here, feel free to comment or correct. So, the individual cells that make up the battery pack have a minimum and maximum voltage range over which they should be discharged down to and charged up to. The cells are not all perfect so some will discharge and charge at slightly different rates. One of the jobs of the Battery Management System is to control this charging and discharging and balancing. The BMS is most likely designed to never discharge a battery beyond its minimum. Therefore it has to provide constant voltage by 'borrowing' from other cells once some cells approach their minimum. An bad BMS algorithm would result in a badly imbalanced battery. There will be so many cells that are at, or near their minimum voltage that there wont be enough cells for the BMS to provide the constant voltage and we will see voltage sag. Combine this with the lower ranges due to the cold weather and this effect happens very soon in the discharge cycle of the battery. So, it is more important to have a fully balanced battery in cold temperatures so that the BMS can provide a constant voltage for the longest time from a set of near equal cells. So, even after the new BMS algorithm is applied, it will take many charge/discharge cycles to correctly balance all the cells, so until that time, the voltage sag will happen early in the discharge cycle.

Thanks for the detailed explanation but for me at least I can see 450v after a full charge and balance, so this suggests all the cells are equal. Maybe it could be something to do with the discharge algorithm at low voltage that's incorrect?

 

[DriverInNorway]

Thanks for the detailed explanation but for me at least I can see 450v after a full charge and balance, so this suggests all the cells are equal. Maybe it could be something to do with the discharge algorithm at low voltage that's incorrect?

Mmmmm, yes, guess that does mean the battery is balanced. So, I guess, either the power reduction is by design or the cells discharge at very different rates. Looks like it is by design and so if it is still present when I get my car back, then it is not acceptable. Like you say, we should see a constant power delivery throughout most of the batteries capacity.

 

[AndyNWuk]

I had the new BMS January 2021 update done today and drove back from Burnley to Blackpool with around 70 miles left on the charge.

I have to say the car performed extremely well maintaining a steady 70mph to 75mph in places all the way home without a flinch.

I put the car on charge this evening using my ROLEC Dumb charger and it took around 4 hours to get it up to 100% charge, but for some strange reason, the indicator light on the ROLEC remains green instead off a steady blue which is normal once the battery is fully charged.

It is now another 4 hours further on and have just checked the car which is still saying 100% charged but the green light still remains on as though the car is still receiving a charge.

The MG Logo remains stable and not pulsating, I have completely shut down the Rolec supply and resumed it again and unplugged the charging lead and re-connected it etc. and each time it goes green which tells me the car is still pulling some charging current even if small.

Is this maybe the process of equalisation of the cells?

Will leave it overnight and check again in the morning and if still green will call the dealer to see if they can shed some light on the suspect problem.

Unless of course anyone else out there have experienced something similar since the BMS latest update.

Andy (Blackpool)