MG5 LFP SOH Drama (88%) vs. Real Physics: Why the Display Lies (Experience Report + SIPS Updates)

[Jyrgo]

Hi everyone,

I’m sharing a deep dive into the SOH of my MG5 Standard Range (LFP, 50.3 kWh ,2022 facelift). As an electrical technician, I trust metered data over software estimates. My case is a perfect example of why you shouldn't panic over a dropping SOH display.

The Data:

• Vehicle: MG5 SR, ~70,000 km.
• SOH Display (BMS): 88.18% (via Car Scanner).
• Cell Health: Delta at 17% SOC was only 6 mV; at 85% SOC, it was a staggering 1 mV. Chemically, this pack is in "like-new" condition.

The Metered Proof:I performed a calibration charge from 8% to 100% SOC. The charging station meter showed exactly 47.74 kWh delivered.

The Math:

1. Charging 92% of the battery (8 to 100) means a full 0–100% charge would pull 51.89 kWh from the grid.
2. Even with a realistic 13% charging loss (AC/DC conversion, 12V overhead, cooling), that means approx. 45.1 kWh was actually stored in the battery.
3. A factory-new MG5 has a usable capacity of ~46 kWh.
4. This puts my real-world capacity at roughly 98%, completely contradicting the BMS claim of 88.18% (which would mathematically only be ~40.5 kWh).

Software & Range:I have updated the BMS along with several other key modules to the latest 2026 software baselines. I am still observing whether the range calculation has become more accurate as a result. Currently, at 85% SOC, it shows 245 km of range (with an average consumption of 16.0 kWh/100km). The SOH display remains very sluggish and seems to take a long time to reflect the new data.

Am I wrong?

 

[Neil MG5 in portugal]

That’s interesting — I have a 2022 facelift with the 50kWh battery showing the same SOH at 88%, and the car has only done just under 40,000 km.

After a recent service, I asked MG if this was normal. They said it was on the low side and suggested that, as the car was imported with no MG service history, it’s quite likely the mileage is actually higher. However, on a full charge the car predicts around 320 km, although I’m not sure what the real-world range actually is.

So would measuring how many kWh the battery takes during a full charge be a more accurate way of determining the true SOH?

 

[MickeySw]

My case is a perfect example of why you shouldn't panic over a dropping SOH display.

Generally speaking a ‘wrong’ SoH value will affect the performance of a battery: current capacity = maximum usable capacity x SoH x SoC

In your case around 40.5kWh. The car will shut down once this capacity is ‘used’ up even if there is another 5kWh left in the tank??

The SOH display remains very sluggish and seems to take a long time to reflect the new data.

SoH isn’t updated by trip data; it simply reduces over time following a pre-programmed degradation model (age, no of charge cycles etc).

It’s recommended to do a regular BMS calibration to make sure the theoretical value and the measured data match.

If they have drifted apart, multiple battery calibration charges, I.e discharge below 10% then AC charge without interruptions to 100% and let balancing complete, might improve SoH.


Having said all that, I wouldn’t be too concerned as MGs SoH calculations for LFP batteries seem to be ‘all over the place’…

 

[Jyrgo]

If your car predicts 320 km at 100%, it effectively disproves the 88% SOH.

A true 88% SOH would mean your usable capacity is down to ~40.5 kWh, which would make a 320 km range prediction impossible at normal consumption levels. Your VCU (Range Calculator) clearly sees a full battery, while your BMS is stuck on a 'pessimistic' software plateau.
The dealer's comment about the mileage is a typical deflection. Since we both see exactly 88% despite having a 30,000 km difference in mileage, it's clearly a software logic issue, not physical degradation.

To answer your question: Yes, measuring the kWh at the charging station is far more accurate. Here is the math you can use:
Note the energy delivered by the station (e.g., 47 kWh).
Subtract approx. 13% for charging losses (OBC efficiency, thermal management, 12V systems).
If the result matches the usable factory spec (~46 kWh), your battery is physically at 100% health, and the SOH display is simply lying to you."