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.