MG4 51kWh LFP Battery Health

[ReintjeWA]

I’m a little surprised people care so much about battery health being as close to 100% as possible. You never hear this from ICE vehicles, even though we all know they lose power over their lifespan, but there it’s just accepted as part of the deal.

I don’t really worry about the state of my battery beyond what the range is when I need to get somewhere. If I was worried the battery won’t hold out sufficiently until I sell this car, I wouldn’t have bought it.

To me this falls into the same category you see with hyper miling and maximum range figures. I just drive the car and charge when I need to, it’s already so much cheaper than petrol, and that’s with using public chargers. Soon as we move and we can charge at home I doubt I will ever worry about maximum range / minimum kWh/km

Edit; I understand the interest in SOH from a “I’m just interested” standpoint, just don’t get it from a “I need it to enjoy the car” standpoint.

 

[MeGatron4]

I think you're wrong there, it may not be an issue in your particular use case, but if someone uses this car for ubering patrons or regular travel between jobs as a self employed contractor that effect is going to be a lot more pronounced and you want the best ROI you can get if it's a business purchase. Also it's the equivalent of knowing how to check the oil and water on an ICE car as well as tyre pressure for maximum range. Cars aren't a cheap investment, you want to look after it and delay the purchase of another one for as long as possible. Unless you're trust fund baby or something.

 

[ReintjeWA]

I think you're wrong there, it may not be an issue in your particular use case, but if someone uses this car for ubering patrons or regular travel between jobs as a self employed contractor that effect is going to be a lot more pronounced and you want the best ROI you can get if it's a business purchase. Also it's the equivalent of knowing how to check the oil and water on an ICE car as well as tyre pressure for maximum range. Cars aren't a cheap investment, you want to look after it and delay the purchase of another one for as long as possible. Unless you're trust fund baby or something.

If it’s a business purchase you should be on top of your depreciations and you’ll be replacing it way sooner than a private owned vehicle. I think investment is also a misnomer as it is a depreciating asset.

If you need the absolute maximum range for your job or business, and you need to drive around with hyper inflated tyres, only travel with the wind in your back and never have any heating or cooling, you obviously didn’t do your due diligence and bought a car with the wrong battery. You would say the same to someone who’s trying to move a big boat on a trailer in a Hyundai Getz.

I’m no trust fund baby, but I also don’t worry about keeping what I own in pristine condition for some stranger in the future.

 

[T1 Terry]

I can understand that an Uber driver would go for LFP over NMC cells and be interested in the SOH of the battery ..... but you need to understand that the figure the MG computer is proving is ..... a bit like the Windows progress bar when it has a bigger job to do ..... it's "give or take half a brick" at best.

Once the true battery capacity is established, it would be great if that could now be set as the true 100% SOH and deterioration could be established from that point ...... but that's never going to happen any time soon.
The more often you top balance the battery with LFP cells, the closer to an accurate 100% SOC you will get. Cell balancing, as shown in the post by Everest, can only occur when a cell gets ahead of the others voltage wise. I expect the MG uses the lossy method of burning the excess off with a resistor to turn Ah stored into heat .... at a very slow rate, so it will take lots of trips to fully charged for that high voltage cell to have the top trimmed off so the others can catch up

T1 Terry

 

[T1 Terry]

One of the things that really gets under my skin, is people being experts on a subject by reading other people's papers without diving into what was actually happening, and making it up as to what they believe is happening.

The first parameter that needs to be understood, the upper cell voltage stop charging limit

The second is understanding the lower stop discharging limit.

The third parameter is allowing the voltage to settle after both charging and discharging, this also allows the heat to escape from the cell.

The fourth and all important one is, electrolyte temperature

The assumption he made, that lithium ions are lost, isn't supported by any actual studies. What is seen is higher temperatures lead to faster electrolyte degradation, the lighter bits in the petrochemical electrolyte carrier fluid become separated into a vapour, this is the "smoke" some claim to see coming out of an over charged battery, also responsible for that sickening smell. Once these compounds are lost from the electrolyte, the less electrolyte there is in there to saturate both the material and through the separator, so the ions can move from cathode to anode and back again. If you have less area of the plate saturated in electrolyte, you have less area to store and retrieve these lithium ions ...... so you loose capacity. It isn't like a flooded cell lead acid battery, there isn't a heap of electrolyte sitting above the plates to act as a back up, there is just enough to keep the plates wet while the cell case stays the shape it is ..... another topic for anther ramble

The other issue is the junk left over from these lighter compounds, after they boil off, coats the faces of both the anode and cathode. This makes it harder for the lithium ions to get through, so they need a greater push .... this is the increased resistance seen in an aging cell, simply the higher voltage required to move the lithium ions in and out of the cathode or anode and into the electrolyte.

The lithium ion does not travel from the anode to the cathode and back as such, but rather it's like those crazy swinging ball toys you see on a head shrink's desk, a lithium ion leaves one side plate and forces a lithium ion to get out of the mix on to the other plate, either getting it self tucked in between the graphite "blanket" facing, or recombining into the lithium ferrous phosphate material on the other plate. Once there are no more lithium ions to eject from the LFP material, it would become ferrous phosphate ...... but that is never likely to happen, there are a lot more lithium ion available than spots to put them in the graphite plate.


I'll stop again, I think I might have over done it this time, I can hear the ZZZ flying out the windows from here

T1 Terry

 

[ReintjeWA]

I'll stop again, I think I might have over done it this time, I can hear the ZZZ flying out the windows from here

T1 Terry

I don’t really have the knowledge to understand a lot of this stuff, but I do enjoy seeing someone knowledgeable explaining things.

It reminds me I know enough to realise how little I know about batteries.

 

[T1 Terry]

Thank you, the learning curve was near vertical for me some 12 yrs ago, there didn't appear to be anyone who knew just what they were talking about. It has only been through hands on work and some 200 systems out there over the last 12 yrs giving feed back to understand what I now share with anyone who wants to read it.

The really tech stuff I owe to Professor Jay Whitacre when he was at Carnegie Melon University producing a video for the people getting into the EV conversion industry way back when , unfortunately, I can't find this You Tube Video and I lost my copy when I lost my computer and back ups when both my house and my motorhome burnt to the ground

T1 Terry

 

[ReintjeWA]

The really tech stuff I owe to Professor Jay Whitacre when he was at Carnegie Melon University producing a video for the people getting into the EV conversion industry way back when , unfortunately, I can't find this You Tube Video and I lost my copy when I lost my computer and back ups when both my house and my motorhome burnt to the ground

T1 Terry

You should email him (Whitacre Research Group| People) and ask if he has a copy or link he can send you. I bet he'd be chuffed to help you out, I know I get super excited when my students have questions. (And I'm pretty sure they use this against me as a work avoiding tactic.)

 

[Everest]

IMHO, we don't know what algorithms SAIC use to create a SOH value.

But I am sure MG will have implemented a line of code in their BMS that looks something like...

if ((vehicleAge < 8) && (Odometer <100,000))
{
   minimum_SOH = 71;
}

 

[decrep]

The lithium ion does not travel from the anode to the cathode and back as such,


I'll stop again, I think I might have over done it this time, I can hear the ZZZ flying out the windows from here

T1 Terry

Just when I was getting interested, wasn't me snoring!

 

[T1 Terry]

Maybe we should start a new thread, you, or anyone, asks a question and I answer it to the point everyone has dozed off .... or I catch myself getting too techo and stop, then you can ask for more clarification where I got so deep you couldn't follow it .......

Sound like a plan?

T1 Terry

 

[siteguru]

Probably best in the General Chat board too, as it won't be MG4-specific.

 

[MG4London]

How do you check the battery health?

 

[Bam Bam]

How do you check the battery health?

Several ways:

1. The dealer tells you at a service (don't know if accurate or not).
2. You can get an OBD dongle to connect the car to your phone and an app to.
3. You can get a more detailed report from a specialist company.

Or you could do it the manual way by filling it right up, driving it until it runs out, filling it right up again and then seeing how much energy it used.

 

[tsedge]

It isn't that useful to get a SOH number, because we don't know how it is calculated (and the calculations may change after software updates) or what it really means. Real-world range testing with same journey and comparable conditions is the best way to figure out something useful as BamBam suggests.

 

[MelanieMoxon]

Attached is mine from car scanner, At my recent service (via MG) I was told that my SoH was 100%



View attachment 32966

The dealer may be reading the wrong value, my Trophy has 14,500 miles on it at the last service and the dealer told me the SOH was 90%, which if true is worrying for an NMC battery.

 

[stevegus]

I have the same battery in my LR and 4 days ago at 15,500 it has 96.9% capacity.

Measured with carscanner app and obd dongle

 

[baader]

Hi, does the MG4 not have a battery temperature sensor? I couldn't find this value in either the MG Smart app or the Home Assistant integration. Yet the vehicle has two battery heating modes right away, but it's strange not to find out what the battery temperature is anywhere.

 

[siteguru]

Car Scanner via an ODB2 dongle can read battery temperatures.

 

[Tig170]

Update, Gen 1 (Sept 22), nearly 30k miles - Recent service Main Dealer = SoH = 100%, below is from car scanner - Basic 51kW SE