YouTube comment about MG4 battery management, LFP vs NMC

[Rolfe]

I came across this comment on a YouTube video by a commentator going by the handle of NIanais.



I'll quote the important part here. (She - I assume she, because of the feminine avatar - also goes on to criticise MG's customer service, in terms we're all familiar with.)

To begin with, we must stop confusing the two battery chemistries at the BMS software level. The BMS degrades the LFP battery by following a schedule of -0.01% every day, whether the car is used or not. While the NMC remains at 100% even after a year of use and more than 30,000 km. So there is a big BMS charge manager problem.

The second important point is intelligent heating. Here too, MG confuses the two chemistries. An NMC needs just over 10 degrees Celsius to start charging in high speed, while LFP chemistry requires 25 degrees Celsius to charge quickly. The problem is that MG has introduced a battery heating start threshold for both versions at less than 10 degrees, which slows down charging and damages the chemistry at the same time. CATL tested these batteries before delivering them to MG, which was unsure how to properly integrate them into the car. The proof is that CATL indicates that the charging power can reach 117 kW. Tesla also sources from CATL, and their charging speed is more than adequate. So, when you hit the road for a long journey, it's a disaster with this MG4S 51 kW because of the battery heating which never turns on before a charging station, since the average temperature while driving remains above 10 degrees.

This is way above my pay grade, but does anyone have any clue what she's on about?

 

[siteguru]

She's basically saying that minimum optimum temperature for rapid charging with the LFP pack is 25C, but as the BMS is essentially "coded" for the NMC pack (which requires 10C minimum) then the LFP pack will rarely be at optimum temperature when you arrive at a DC charger - even with Intelligent Battery Heating enabled - hence why you'll never see the 117kW charge rate per the original specs.

I'm not sure about the -0.01% degradation per day comment though re. LFP pack. That would mean the LFP pack degrades 3.65% every year (regardless of use), so after 5 years the SOH would be about 82% ... I am very sceptical about that.

"She" seems to aver that she speaks from a position of knowledge ... but then anyone on the Internet can read stuff and copy/paste to make themselves seem to be an "authority".

 

[fnegroni]

She's basically saying that minimum optimum temperature for rapid charging with the LFP pack is 25C, but as the BMS is essentially "coded" for the NMC pack (which requires 10C minimum) then the LFP pack will rarely be at optimum temperature when you arrive at a DC charger - even with Intelligent Battery Heating enabled - hence why you'll never see the 117kW charge rate per the original specs.

I'm not sure about the -0.01% degradation per day comment though re. LFP pack. That would mean the LFP pack degrades 3.65% every year (regardless of use), so after 5 years the SOH would be about 82% ... I am very sceptical about that.

"She" seems to aver that she speaks from a position of knowledge ... but then anyone on the Internet can read stuff and copy/paste to make themselves seem to be an "authority".

One thing to remember is that the LFP pack takes a long time to warm up too, therefore if you plan to DC charge and you know the battery is cold, you should pre heat it about one hour before you dc charge. I don’t dc charge often enough but when I have done during the recent cold spell it got near enough to 80kW even at around 25% charge but ensuring the battery is preheated.

 

[Edward Xuereb]

Is battery heating required if one charges the MG4 using a 7kW single phase charger?

 

[Matt x power]

Is battery heating required if one charges the MG4 using a 7kW single phase charger?

No only for super fast charging

 

[Rolfe]

I've seen 85% on mine without any attempt to warm the battery. It was summer though, and in England, so 25°C could be possible.

 

[salty]

I came across this comment on a YouTube video by a commentator going by the handle of NIanais.



I'll quote the important part here. (She - I assume she, because of the feminine avatar - also goes on to criticise MG's customer service, in terms we're all familiar with.)

To begin with, we must stop confusing the two battery chemistries at the BMS software level. The BMS degrades the LFP battery by following a schedule of -0.01% every day, whether the car is used or not. While the NMC remains at 100% even after a year of use and more than 30,000 km. So there is a big BMS charge manager problem.

The second important point is intelligent heating. Here too, MG confuses the two chemistries. An NMC needs just over 10 degrees Celsius to start charging in high speed, while LFP chemistry requires 25 degrees Celsius to charge quickly. The problem is that MG has introduced a battery heating start threshold for both versions at less than 10 degrees, which slows down charging and damages the chemistry at the same time. CATL tested these batteries before delivering them to MG, which was unsure how to properly integrate them into the car. The proof is that CATL indicates that the charging power can reach 117 kWh. Tesla also sources from CATL, and their charging speed is more than adequate. So, when you hit the road for a long journey, it's a disaster with this MG4S 51 kWh because of the battery heating which never turns on before a charging station, since the average temperature while driving remains above 10 degrees.

This is way above my pay grade, but does anyone have any clue what she's on about?

Not a clue.

She's basically saying that minimum optimum temperature for rapid charging with the LFP pack is 25C, but as the BMS is essentially "coded" for the NMC pack (which requires 10C minimum) then the LFP pack will rarely be at optimum temperature when you arrive at a DC charger - even with Intelligent Battery Heating enabled - hence why you'll never see the 117kW charge rate per the original specs.

I'm not sure about the -0.01% degradation per day comment though re. LFP pack. That would mean the LFP pack degrades 3.65% every year (regardless of use), so after 5 years the SOH would be about 82% ... I am very sceptical about that.

"She" seems to aver that she speaks from a position of knowledge ... but then anyone on the Internet can read stuff and copy/paste to make themselves seem to be an "authority".

That's cleared it up for me.

 

[hharzel]

CATL tested these batteries before delivering them to MG, which was unsure how to properly integrate them into the car.

Not meaning to be harsh, but that sounds like something I would expect of MG. BMS configuration is a software thing so I wouldn't be surprised if they managed to mess it up too. The fact that my car is regenerating mildly even below -20° celsius when it certainly should not corroborates that. It is either a bug or a BMS misconfiguration.

The consensus is that LFP lasts longer than NMC but in my opinion, given that LFP has a much lower fire risk, manufacturers are now able to squeeze out every last bit of the battery pack at the expense of its health and therefore LFP will probably wear out quicker, especially in colder environments. Data will show in the years to come. People don't like to wait for the battery to warm up when they have a long journey to make. Maybe that -0.01% is there to compensate for excessive lithium plating, just to be on the safe side, if there is any truth to the claim?

As long as the battery's health is above 70% after seven years all is well for MG.

 

[Matt x power]

Nmc will be very reliable if you look after it

 

[unbornidentity]

The part about “The BMS degrades the LFP battery by following a schedule of -0.01%” is probably to do with the difficulty of determining the state of charge of an LFP battery. NMC battery SoC is calculated from the voltage but LFP batteries stay at around 3.7 volts no matter what the state of charge is. That is why the manual recommends charging to 100% at least once a week and discharging to less than 10% every 3 months. It helps the BMS calibrate, so you don’t suddenly lose range due to miscalculation. Tesla recommends charging to 100% every time on LFP cars and has removed the option to set it the charge at everything apart from 100% and 50% for long term storage.

LFP batteries actually degrade at about half the rate of NMC and because they are at a much lower voltage at 100% can tolerate being charged to 100% all the time. The only time you should avoid it is when you’re leaving it at high ambient temperatures.

LFP batteries are worse than NMC batteries when it comes to charging at low temperatures but at 10°C the charge rate should be fast enough that the act of rapid charging should warm the battery pretty fast.

If I lived in Canada or somewhere where it gets really cold regularly then I’d not want an LFP battery. In Europe it’s not really a big problem.

Mind you I’ve not needed to Rapid change my MG4 yet. But I did try to rapid charge my Cupra in winter and the battery heater was disabled on that and below 0°C even AC charging slowed down!

 

[Rolfe]

We've got a bunch of members in Norway and Finland who might dispute that it doesn't get really cold regularly in Europe!

 

[Rolfe]

I'm kind of "faint but pursuing" here. I'm not sure I really understand it all though.

 

[salty]

I'm kind of "faint but pursuing" here. I'm not sure I really understand it all though.

I'm pretty sure I don't.

 

[unbornidentity]

We've got a bunch of members in Norway and Finland who might dispute that it doesn't get really cold regularly in Europe!

I don’t understand your terminology but I suppose if people had loads of problems in Norway or Finland they would say.

Or maybe they don’t go for LFP or maybe they are better educated about electric cars so know all about preheating.

 

[Rolfe]

There's a Finnish member posting above who has an SE SR and seems perfectly happy with it while reporting temperatures of -30°C. Although he (or she) has said the range has halved and the battery heating is on all the time.

 

[salty]

I don’t understand your terminology but I suppose if people had loads of problems in Norway or Finland they would say.

Or maybe they don’t go for LFP or maybe they are better educated about electric cars so know all about preheating.

Or maybe they don't moan as much.

 

[Rolfe]

Having read the posts from the Finnish members, I'd say they're better educated about EVs than some people in America seem to be, and they know all about preheating.

 

[Ian Key]

Having read the posts from the Finnish members, I'd say they're better educated about EVs than some people in America seem to be, and they know all about preheating.

That's true and not just EVs

 

[JonnyG]

Anyone know the length of the battery warranty on the MG4 ? I was speaking to some "high milers" in an MG4 Trophy at a charging station and they reckoned it was 7 years or 80,000 miles - whichever came first. I was a bit shocked at the 80,000 miles - is that right ?

https://www.mg.co.uk/sites/default/files/2021-10/MG_Online_Warranty_Statement_October_2021.pdf

 

[siteguru]

This is what the warranty states:

Warranty Period
The warranty period commences on the date of first registration. MG covers vehicles (registered on or after 01/09/2019) for unlimited mileage up to 12 months, and for 80,000 miles between 13 months and 84 months (whichever comes sooner). The warranty transfers to each new owner so long as it has not expired.

So anything not specifically excluded with shorter warranty periods/mileage limits (which are listed in the document) are warrantied for unlimited miles in the first 12 months, and for 80k miles in the following 6 years. So, technically, the warranty mileage is whatever you've done in the first year plus a further 80k miles.