Test your MG4 battery to understand low range

[hojnikb]

There's couple of things wrong with your method;

First as noted before; your battery doesn't actually have 77kWh of usable capacity. The actual value when new is 74.4kWh.
Secondly, the usable capacity also includes bottom buffer (which should be a couple of kWh on this model). When GOM says 0% it's not actually 0%. You need to drive the car until it shuts off to actually get the "full" capacity of the pack.

Batteries also lose it's usable capacity thru heat, as they have internal resistance thats more than 0ohm. So if you have 74.4kWh nominal, at for example 0.5C rate, the actual energy you get out is maybe just 73-73.5kWh and else is lost via heat.

And the last point; Are you sure the kWh/100km meter actually accounts for all power usage in the car? If not, your calculation will again be skewed. To get the most accurate value, you'd have to charge to 100%, balance and then discharge the pack via external means and count the kWh going out. This would be irrefutable evidence, that battery capacity is not correct.

But i suspect everything is ok and your methods are poor.

 

[MrSkyBlueCar]

Regarding the kWh/100km figure: is that measured as the energy supplied by the battery, or the energy put into the motor?

Because if it's the latter (and I suspect it is), then it doesn't include all the energy used by the rest of the car's systems (aircon, lights, power steering, etc), and it also doesn't include losses.

As you'll be well aware, no system is 100% efficient, so some of the energy supplied by the battery will be lost to heat and noise.

 

[Evergreen]

Yep, just like the German guy thinking he can sue MG regarding open source software that MG isn't 'releasing'. Some people always angling to become a 'peoples' hero when they are in fact completely deluded themselves for various other reasons.

@Evergreen, thank you for replying to my post, I now understand where you are coming from.

If I have understood you correctly, you are using the figures displayed by the car. So, do you know how those figures are calculated and what rounding actions are taken?

Please confirm that, for your calculations, you have completely charged and balanced the car and then driven continuously to zero charge with the car finally giving up.

I ask this because I have found that the miles/kWh figures only give an acceptable answer for single journeys. When I use the figure after carrying out many small journeys it gives a capacity figure well down from the specification of my Trophy LR.

Note I multiplied up from a 10% battery level drop for the matching mileage - on 3 occasions over the same route - to calculate the answer near to the battery specification.

Search for 'Battery level not match with consumption figures' in this forum for more discussion of this topic.

Thanks for your input
Another issue is that the % charge left indicators is very non linear. It’s skewed to make the mileage look good when the car is more than 50% full

There's couple of things wrong with your method;

First as noted before; your battery doesn't actually have 77kWh of usable capacity. The actual value when new is 74.4kWh.
Secondly, the usable capacity also includes bottom buffer (which should be a couple of kWh on this model). When GOM says 0% it's not actually 0%. You need to drive the car until it shuts off to actually get the "full" capacity of the pack.

Batteries also lose it's usable capacity thru heat, as they have internal resistance thats more than 0ohm. So if you have 74.4kWh nominal, at for example 0.5C rate, the actual energy you get out is maybe just 73-73.5kWh and else is lost via heat.

And the last point; Are you sure the kWh/100km meter actually accounts for all power usage in the car? If not, your calculation will again be skewed. To get the most accurate value, you'd have to charge to 100%, balance and then discharge the pack via external means and count the kWh going out. This would be irrefutable evidence, that battery capacity is not correct.

But i suspect everything is ok and your methods are poor.

I’ve checked this. The only non driving significant use of power is the ptc heater and to some extent the aircon. Both do affect the kWh. And if any excuses are true, why didn’t local dealers, mg nz or mg Australia simply tell me that? Their silence speaks volumes

 

[hojnikb]

I’ve checked this. The only non driving significant use of power is the ptc heater and to some extent the aircon. Both do affect the kWh. And if any excuses are true, why didn’t local dealers, mg nz or mg Australia simply tell me that? Their silence speaks volumes

Unless you can actually prove that the battery doesn't have the stated capacity (including your degradation) you'll have a tough time proving anything...

Like I said above; short of discharging the battery externally, it will be difficult to prove anything properly.

 

[Martinonline]

Thanks for your input
Another issue is that the % charge left indicators is very non linear. It’s skewed to make the mileage look good when the car is more than 50% full

I think you will need to justify this statement.

As regards my other question, you have not said whether or not you have carried out a 100% discharge in a single journey and used the car's figures for your calculations.

As an aside, I would have thought it would be easy for MG, or any EV manufacturer, to fudge the figures to always lead to a calculation solution matching the specified battery capacity. The fact that that does not always happens means that MG is confident of its specification or it has missed a trick.

 

[HazardLights]

@Evergreen We don't know the formula, method and precision of the calculations for the summary statistics. Therefore we don't understand the precision, and compounding of errors of the derived values. Batteries are complex analogue systems and the methods for counting things are imperfect. The methods of testing here will also damage the batteries capacity although I couldn't tell you the degree of harm.

I think that more people would agree with your conclusions if you find prima face case using OBD and if the battery aging was unreasonable given it's use and treatment then corroborated the findings with professional lab testing. Anything short of this would be ripped to shreds in court.

EVs are new to many dealers and customer knowledge often exceeds staff. It shouldn't be this way but it is. This in itself isn't proof of fraud or shoddy goods.

My LR battery at 12000 miles is showing a 99.8% State of Health.

 

[gary333]

I wonder if in your case it would be worth getting a portable battery pack and leaving it in the boot so you can actually drive the car down to empty and then charge it back up once it conks out (once it's been fully charged to 100%).

I've managed to get 249.1 miles from my 64kwh model, with a quoted 4.2mi/kwh, although I only took it down to 2%. This equates to a 60.5kwh battery capacity if the scale is linear at 100% (i doubt it's linear though). It does feel like in my case the car is likely to have it's quoted 62.1kwh battery capacity if I were to drive it around on 0%, which makes me wonder if maybe your car just needs to be fully emptied to reset the BMS.

 

[SteveM]

An interesting discussion. When I first got my MG4 I was puzzled by the mi/kWh figure. I use the car for a commute, so the journey is pretty similar every day. As the seasons changed it became obvious that the mi/kWh figure is highly temperature dependent, much more so than might be expected from temperature dependent efficiencies in the power train (oil viscosity?), or any change in air viscosity.
The miles part of the measurement should be straightforward, presumably based in the total number of wheel revolutions, with maybe minor errors if the tyres are under-inflated. I had at first thought that the kWh was a simple integration of the power supplied; such an electrical measurement would be easy. However, the observed temperature dependence implies that the kWh is actually an estimate based on the remaining battery capacity. In other words, like a fuel gauge for a miles/gallon figure given in an ICE car. Someone on this forum probably knows if I am correct.
Measuring remaining liquid fuel is not difficult in principle; it a direct measurement of the quantity quoted in the consumption figure. However, measuring the battery capacity is not straightforward, as it can only (presumably) be based on the cell voltage, which undergoes a relatively small change. Moreover, the real capacity depends on, temperature at the time of measurement (I guess) and also a prediction on how power will be taken in the future. If I am correct the displayed figure does take all the ancillary consumption into account, i.e. Evergreen's calculation is valid in that sense, but I would expect a pretty large uncertainty.
My opinion is that Evergreen's claim should certainly fail, given a technically competent judgement. In any case, the value that matters is not battery capacity but range. If in mild weather, on level roads, at reasonable speed (say 40 MPH) they could not achieve the quoted range, there might be a valid complaint.

 

[Starplots]

Your formula is faulty. The kWh per 100km is a rolling average. When you took that figure at the 0% mark, it only gave you an estimate based on the last few km driven.

 

[MrSkyBlueCar]

As the seasons changed it became obvious that the Mi/kWh figure is highly temperature dependent

Yes, that's a feature inherent to batteries. Batteries are dependent on chemistry, which is dependent on temperature. This is why EVs lose a chunk of their range in the winter. Their capacity (in kWh) doesn't change, but their efficiency does.

 

[adiel]

Measu

Very simple.
Fully charge
Zero the accumulated journey recorder
Drive till battery % is zero
Then you have used all the useable capacity as the car is no longer safely drivesble
The car displays distance covered and kWh per 100km (or maybe per 100 miles in some areas).
Multiply the two together and divide by 100 gives you the kWh you’ve used.
In my case it’s always around 67 whereas the spec is 77
Method and type of driving and weather etc does of course affect the estimated range but not the real capacity.
Try it yourself and if you find the same as me you have a very valid complaint, actionable in most legislations.

When the car states 0% on the GOM, that doesn't mean the battery is totally depleted. Think you'll find you still have some significant range remaining. Also, most manufacturers state a gross and usable battery capacity 77kWh is the gross battery capacity of the MG4 Extended Range but the Useable capacity is 74.4 kWh, with the difference between gross and usable reserved by the BMS to do it things and balance cells etc. You may also be ignoring charging losses in the conversion of energy from AC to DC i.e. what you charger puts into the car is not equal to what it stores and ignoring driving styles/road conditions/speeds/temperature. To achieve WLTP combined range, an MG4 Extended Range should average 4.34 miles per kWh. From my own experience, which is heavily skewed towards UK motorway driving all year round, my average is just over 3.6 miles per kWh, which I am entirely happy with.

 

[SteveM]

Your formula is faulty. The kWh per 100km is a rolling average. When you took that figure at the 0% mark, it only gave you an estimate based on the last few km driven.

Why do you think that?
The range is based on recent consumption rate, but surely the mi/kWh is an average value since the last trip reset.

 

[Roger001]

As a side note, trying to use the car's own tools for measuring distance (and speed) is also a problem. The car does not use GPS, instead just the number of wheel revolutions. So the recordings depend on the amount of tread on the tyres. New tyres have a larger diameter than old tyres and so need to do fewer revolutions for any particular speed.

The only way you can truly measure the battery capacity is to connect test equipment directly to the battery that charges, discharges and then charges the battery in a consistent, controlled way.

All EVs are sold with the batteries being marketed at their 'device' capacity, which will never be what you see using the car's own reporting as there are losses and inconsistencies that the reporting can not account for.

 

[tsedge]

Regarding the non-linearity of the charge remaining indicator...

Mine is actually much better than most ICE vehicles I have owned, many of which stuck on "F" for around 100 miles, then dropped slowly to "1/2" over the next 200 and then from "1/2" to "1/4" in another 50 miles at an increasing rate and then dashed to "E" over the final 30.

MG's may not be linear but I find it easy to adjust for the faster drop off towards the end.

 

[Cabansail]

The issue, as I see it, is with the calculation and method used.

1. The accuracy of the measuring equipment used is not reliable. The instruments in the car are advisory only. To be taken seriously in court you would need to use verifiable scientific measuring equipment.
2. There has been no allowance for efficiency. In every system there are losses due to energy conversions, transmission etc. Your test method compares the battery capacity to the energy delivered. The energy efficiency needs to be included.
3. As previously stated there will be some retained energy in the battery even when in hits the cut out.

If we accept the figure of 67 kW-hr you calculated and a capacity of 77 kW-hr that is an efficiency of 87%. Take into account the other factors and this would probably rise to over 90% efficiency. Those are very good figures.

 

[GoElectric]

Your litigation has no legs to stand on. To just have some basis, you will have to invest serious money to scientifically test the battery as to what kWh capacity it has under certain conditions. The total energy that battery can output depends greatly on the discharge rate and other factors such as outside temperature, age etc.

I think you just have poor throttle management with regen set on Low and/or drive predominantly on highways, A/C temperature settings, battery pre-heating, driving well above 115 km/h ergo discharge rate affects the "total capacity" when you calculate with GOM.

Also, have you figured out how driving modes work internally? Why is there less km of range, if you drive with same accelerations and speed in a sport mode? There are so many variables before you even get to the true capacity of the battery. Simply going by GOM will not get you the results you need.

You will have to reverse engineer the whole working process from the battery to inverter coding, GOM calculations. A lot of work.

If you're not satisfied with it and you think you're being sold a lie, just sell the car. I am satisfied with mine and behaves in line with the stated specs.