MG4 51kWh LFP Battery Health

[Semerkand]

Hi everyone!
I'm second owner. It had 10500 (6524 mile) kilometers on it when I bought it and SOH was 93.64% . Now my car is 17500(10873 mile) km and SOH is 93.15%. There is a difference -0.49% in 7000 kilometers. I just wanted to hear your ideas and suggestions. First of all is it normal sitiation?

I don't know the first owner but 93.64 seems a bit low to me.
I must have used home charging for half of the 7000 (4349 mile) kilometers (3.5kW 16A). The rest was long distance, fast charging.

""By the way, i have had the car for 2 months."" that means i lost 0.49% in 2 months.
And and and i really like my car.

 

[Tig170]

Its in the correct range for LFP (using carscanner) - mine started off around 95% and varies +/- 2%, now upto 30k miles.

 

[Semerkand]

Thanks for the reply. I usually try to keep my car at 15-85%. However, I charged it to 100% 3-4 times in 2 months. I heard that LFP is not affected much if charged to 100%, but it is still a precaution. Idk.
So how do you charge yours? And is slow charging better for battery life? any idea?

 

[siteguru]

Have you selected the correct car in your profile? The Comfort spec is like the SE LR in the UK and has the 64kWh NMC battery pack. (Click on the link in your profile for MG4 Comfort and it takes you to the post below).

MG EV Models and trim variations around the world.

Here are the names of the trims of MG EVs used here on MGEVs.com. They are as close to the names given by MG as possible, but with some tweaks to shorten them for use in the forum. SE = Standard Edition SR = Standard Range LR = Long Range ER = Extended Range Battery size is usable as quoted on...

www.mgevs.com

 

[Tig170]

Its good to charge the LFP battery to 100% at it recalibrates itself (I believe), at least thats whats I've seen on my home 20kWh battery system - at home it gets a little lost if I dont charge it to 100% every few weeks.

 

[Semerkand]

Have you selected the correct car in your profile? The Comfort spec is like the SE LR in the UK and has the 64kWh NMC battery pack. (Click on the link in your profile for MG4 Comfort and it takes you to the post below).

MG EV Models and trim variations around the world.

Here are the names of the trims of MG EVs used here on MGEVs.com. They are as close to the names given by MG as possible, but with some tweaks to shorten them for use in the forum. SE = Standard Edition SR = Standard Range LR = Long Range ER = Extended Range Battery size is usable as quoted on...

www.mgevs.com

Sorry i didn't know that. In Türkiye, Comfort spec means 51 kWh one. I corrected it immediately

 

[AlC]

I think it's quite normal for the LFP batteries SOH to drop off fairly quickly in the first year and then then level off after that. I've read the initial drop off is calendar based and programmed into the BMS because it's an expected characteristic of the LFP chemistry.

The other part of it is the 51 has a small buffer. The 64s will often show 100%SOH but that's because there's more available capacity above 64kWh which can be lost before it counts against the SOH of the battery.

I'd only be concerned if your SOH continues to drop off quickly over the next year.

 

[T1 Terry]

The 51kWh is actually a rounded up figure. The 400v can only be achieved by charging the 104 cells to 3.85V ..... that is not how battery capacity or Nom. voltage is measured. The Nom. voltage for an LFP cell is 3.2v x 104 = 333vdc nom. I believe the cell capacity is 125Ah, that gives the pack a nom. capacity of 41.6kWh.
By multiplying fully charged voltage, still only makes 50kWh, so they are also using that built in over capacity that all good LFP cells have, to get the 51kWh number.
Any cell voltage above 3.4V is surface charge, put it under load and that 0.45VDC over charge will vanish, the first bit drawn off the cells will drop the voltage further to around 3.35V x 104 x 125Ah = 43.5kWh, and that capacity you can rely on for quite some time.
Basically, the computer is removing the artificially high capacity rating back to the true capacity by calling it a reduction in SOH, in truth, it's B/S removal ..... Keep that in the back of your mind, and you are seeing the computer determine what the true capacity .... then the SOH will stabilise and this is/was always the true capacity of the LFP battery.

T1 Terry
Edit: fixed the error @ MARTINONLINE pointed out, thank you. If anyone sees any other errors, please point them out, nothing worse than typo errors messing up the information ....

[ Edit Coulomb: But see my post here. ]

 

[Rolfe]

I'm so glad we have you here, Terry!

 

[Rolfe]

By coincidence I just posted this in another thread.

MG4 EV charging

Hello all, I have just taken possession of my first ev an MG4 Trophy long range and I have a question. Is it ok to use a rapid charger on a regular basis as this is currently my only means available to me to charge my car? I am told it may affect the battery life ? Would appreciate your...

www.mgevs.com

 

[T1 Terry]

By coincidence I just posted this in another thread.

MG4 EV charging

Hello all, I have just taken possession of my first ev an MG4 Trophy long range and I have a question. Is it ok to use a rapid charger on a regular basis as this is currently my only means available to me to charge my car? I am told it may affect the battery life ? Would appreciate your...

www.mgevs.com

Saw that, along with the numbers clocking up beside the bell icon on the top right .... I keep thinking I might have gone a bit too far and I'm in trouble but I have to go and have a look so I can sleep later

With the LFP batteries, I started hands on researching them back in 2011, buying $10,000 worth to torture test, mostly because I could believe the amount of mis information on the web, so I had to find out for myself .... ended up starting a business installing them in off grid setups .... well, until they burnt my workshop down .... kind of a forced retirement I guess .....

T1 Terry

 

[siteguru]

Saw that, along with the numbers clocking up beside the bell icon on the top right .... I keep thinking I might have gone a bit too far and I'm in trouble but I have to go and have a look so I can sleep later

With the LFP batteries, I started hands on researching them back in 2011, buying $10,000 worth to torture test, mostly because I could believe the amount of mis information on the web, so I had to find out for myself .... ended up starting a business installing them in off grid setups .... well, until they burnt my workshop down .... kind of a forced retirement I guess .....

T1 Terry

For clarity (for others reading this, especially any anti-EVer) ... the They were of the human kind not the battery kind.

 

[Semerkand]

The 51kwh is actually a rounded up figure. The 400v can only be achieved by charging the 104 cells to 3.85v ..... that is not how battery capacity or Nom. voltage is measured. The Nom. voltage for an LFP cell is 3.2v x 104 = 333vdc nom. I believe the cell capacity is 125Ah, that gives the pack a nom. capacity of 41.6kwh.
By multiplying fully charged voltage, still only makes 50kwh, so they are also using that built in over capacity that all good LFP cells have, to get the 51kwh number.
Any cell voltage above 3.4v is surface charge, put it under load and that 4.5v over charge will vanish, the first bit drawn off the cells will drop the voltage further to around 3.35v x 104 x 125Ah = 43.5kwh, and that capacity you can rely on for quite some time.
Basically, the computer is removing the artificially high capacity rating back to the true capacity by calling it a reduction in SOH, in truth, it's B/S removal ..... Keep that in the back of your mind, and you are seeing the computer determine what the true capacity .... then the SOH will stabilise and this is/was always the true capacity of the LFP battery.

T1 Terry

Learning at least 10 years of experience from here in seconds made me feel really lucky. I am grateful for the information.

 

[Coulomb]

The 51kWh is actually a rounded up figure. The 400v can only be achieved by charging the 104 cells to 3.85V ..... that is not how battery capacity or Nom. voltage is measured. The Nom. voltage for an LFP cell is 3.2v x 104 = 333vdc nom. I believe the cell capacity is 125Ah, that gives the pack a nom. capacity of 41.6kWh.

I would have guessed 128 cells. Then the nominal voltage is a more reasonable 128 * 3.2 = 409.6 V, and the nominal capacity, assuming the same 125 Ah cells, would be 409.6 x 125 = 51.2 kWh.

I think that they would get into big trouble advertising 51.2 kWh when it's really 41.6 kWh, an exaggeration of 23%!

 

[T1 Terry]

I would have guessed 128 cells. Then the nominal voltage is a more reasonable 128 * 3.2 = 409.6 V, and the nominal capacity, assuming the same 125 Ah cells, would be 409.6 x 125 = 51.2 kWh.

I think that they would get into big trouble advertising 51.2 kWh when it's really 41.6 kWh, an exaggeration of 23%!

I found the specs here MG MG4 Electric 51 kWh They use the same battery box for the 64 and 51, the same number of cells in each as far as I can tell ..... yet to remove mine and confirm, but when did battery resellers start being forced to tell the truth? Much like solar panels, you can repeat the specs used for the light box test in the real world, yet they get away with over quoting the output capacity ......

T1 Terry

 

[Coulomb]

I found the specs here MG MG4 Electric 51 kWh

Sigh. That looks like a copy and paste error.

[ Edit: Oops! The above comment was from when I was trying to make Terry's claim of 125Ah cells work, which required about 128 cells. Later I switched to 156Ah cells as the numbers worked out better, and agreed with the MG specs in the link below. I forgot to remove the above statement. ]

Here is a post by one T1 Terry (!) that proves says that we were both wrong:

https://forums.aeva.asn.au/viewtopic.php?p=99996#p99996

So it looks like there really are 104 cells, likely in the same box, but with 156 Ah capacity. They might even be a special run just to fit into the exact same space as the NMC cells. The 327 V "nominal battery voltage" seems to be a fiction to make the actual kWh capacity, nominal Ah capacity, and nominal voltage work out: 327 V x 156 Ah = 51.012 Ah, rounded to 51 kW.

The nominal LFP cell voltage of 3.20 times 104 = around 333 V as you say, but that would overstate the capacity slightly.

when did battery resellers start being forced to tell the truth?

Didn't you get the memo? No more lying by battery manufacturers, inverter manufacturers, solar panel makers, politicians... Oh, wait...

Seriously though, I've always found EV battery claims to be based on actual manufacturer specifications; no exaggeration allowed, it seems. May it long stay that way, and spread to other realms.

 

[Semerkand]

MG MG4 Elektrikli 51 kWh

If my eyes are not lying to me, do I see lithium-ion? Didn't the MG4 standard range have a lithium iron phosphate (LFP) battery type?

 

[Coulomb]

do I see lithium-ion? Didn't the MG4 standard range have a lithium iron phosphate (LFP) battery type?

I'll just point out that technically, lithium iron phosphate IS a type of lithium ion cell. The lithium ions just intercalate into an iron phosphate cathode, instead of into a nickel manganese cobalt or other cathode (I think).

So the EV database is correct to say that the battery type is lithium ion (as opposed to lead acid or sodium ion I suppose), but the cathode type should really say FePO₄ or perhaps FP, rather than LFP. The lithium (in the form of lithium ions) isn't always part of the cathode.

 

[Checo]

I'll just point out that technically, lithium iron phosphate IS a type of lithium ion cell. The lithium ions just intercalate into an iron phosphate cathode, instead of into a nickel manganese cobalt or other cathode (I think).

So the EV database is correct to say that the battery type is lithium ion (as opposed to lead acid or sodium ion I suppose), but the cathode type should really say FePO₄ or perhaps FP, rather than LFP. The lithium (in the form of lithium ions) isn't always part of the cathode.

Sorry to stretch this one out and don't read on if it gets boring. Yes, LFP and NMC are both lithium ion cells with different cathode materials, as opposed to lithium sulfur, lithium air, sodium ion and many, many other quite different types of chemistry that are being researched at the moment. LFP is called that rather than FP because the synthesised cathode material that the cells are made with contains the Li ions, so it is LiFePO₄. During charging the Li ions are deintercalated so it becomes FePO₄, which has a similar crystal structure and only a 6.8% volume difference (one of the real problems with many battery materials) to the LiFePO₄.

Apologies to get a bit technical but research into energy storage materials is what I do...

 

[T1 Terry]

Sigh. That looks like a copy and paste error.

Here is a post by one T1 Terry (!) that proves says that we were both wrong:

https://forums.aeva.asn.au/viewtopic.php?p=99996#p99996

So it looks like there really are 104 cells, likely in the same box, but with 156 Ah capacity. They might even be a special run just to fit into the exact same space as the NMC cells. The 327 V "nominal battery voltage" seems to be a fiction to make the actual kWh capacity, nominal Ah capacity, and nominal voltage work out: 327 V x 156 Ah = 51.012 Ah, rounded to 51 kW.

The nominal LFP cell voltage of 3.20 times 104 = around 333 V as you say, but that would overstate the capacity slightly.


Didn't you get the memo? No more lying by battery manufacturers, inverter manufacturers, solar panel makers, politicians... Oh, wait...

Seriously though, I've always found EV battery claims to be based on actual manufacturer specifications; no exaggeration allowed, it seems. May it long stay that way, and spread to other realms.

That brings the 156Ah x 104 cells x 3.2V into a realm no manufacture seems to venture, as you say, claiming a lower figure for battery capacity. If that were the case, cell and therefore SOH would not be seen dropping at the rate it does over such a short term. All the LYP systems I've installed that come back for their 3 yr service, all test better than 100% capacity at the 0.5C load the manufacturer used for capacity measuring .... in fact, one 12 yr old system still achieve 100% capacity using a 1C test load, stopping at 2.85V under load.

The 156Ah is the questionable part, it doesn't seem likely they would have produced an LFP cell, the same size as a NMC cell, and only 13.5Ah less capacity .... but then, even the 64 NMC pack doesn't add up if the cell capacity is 169.5Ah. 104 cells @ NMC nom. voltage of 3.7V 65.2kWh, yet they called it a 64kWh battery .....

The whole calculation thing actually requires a standard for cell load testing and a definition for nominal voltage.

The best definition I've heard was that the nominal voltage was the average voltage a fully charged cell to under the specified "standard discharge rate" of the cell from 100% SOC to 0% SOC whole still under load. These Winston charts and my own testing seems to support this definition Thunder Sky Winston Water Based Lithium Yttrium Power Battery-Energy Storage-thundersky-winston.com-

T1 Terry