Another Suspicious MG ZS EV Battery Behaviour

Hi all

Following my previous suspicion on my battery. I also notice on a few occasions (tho I do not run into that scenario very often anyway so it could have been more chances of that happened)

I was told from day one that I have the LFP battery (SR 50kwh) which needs to be charged to 100% and not the 20/80 Rule like others. So my habit was to top it up to 100% as and when so very rarely dropped down before 50% anyway.

So here is a thing, last night I left the car at 50% (uncharged), this morning it was at 40% with no preconditioning and no heating set. Did my school run which comprised a 5 mile round trip, came back at 31%..

considering I usually get 15 miles per 10% in this kind of weather and no heating was use , something is seriously not right. And what is more strange is that when it drops to like 25%, from 25% to 15% it behaves back to normal with more acceptable mileage.

Considering the driving conditions are same or very similar, (no heat as well), I cannot work out what went wrong.

And since my car is due for a service next month, can the dealership check for battery health and how accurate is it? and until what state it is considered to be a warranty job if needing for replacement? Just wondering ..

Thanks all

Check out this thread.

The LFP battery doesn't "need" to be charged to 100% every time, it's just more tolerant to it.

SKA said:

I was told from day one that I have the LFP battery (SR 50kwh) which needs to be charged to 100% and not the 20/80 Rule like others.

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No it doesn’t

This is a misunderstanding from some posters on this forum.

If you look at the manual, both batteries have the same recommendations as far as balancing charging for the health of the battery.

Constantly charging to 100% will have a similar degradation effect to the LR. It’s not even more ‘tolerant’ of it.

The only reason MG took off the 80% restriction function is related to the fact it’s a bit more difficult to work out the SoC on LFP batteries, and going to 100% allows the BMS to get a better calibration.

Bodgerx said:

Constantly charging to 100% will have a similar degradation effect to the LR. It’s not even more ‘tolerant’ of it

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Not quite true
LFP Under most conditions it supports more than 3,000 cycles, and under optimal conditions it supports more than 10,000 cycles. NMC batteries support about 1,000 to 2,300 cycles, depending on conditions
There is a big difference so charging it to 100% it will outlast the long range battery but with this advantage there's two big disadvantages

1 BMS unless fully or nearly empty has to guess state of charge
2 LFP really don't like cold weather

I don't even think the charge cycles is biggest advantage I think the biggest advantage it is cost it's a lot cheaper it's also a safer battery

N2STY said:

Not quite true
LFP Under most conditions it supports more than 3,000 cycles, and under optimal conditions it supports more than 10,000 cycles. NMC batteries support about 1,000 to 2,300 cycles, depending on conditions
There is a big difference so charging it to 100% it will outlast the long range battery but with this advantage there's two big disadvantages

1 BMS unless fully or nearly empty has to guess state of charge
2 LFP really don't like cold weather

I don't even think the charge cycles is biggest advantage I think the biggest advantage it is cost it's a lot cheaper it's also a safer battery

Click to expand...

True, I got a bit carried away there. But, charging to 100% all the time will still degrade the LFP battery, just not at the same rate.

I think LFP will become the new norm for cars on the cheaper end of the spectrum, for sure. At least until something cheaper and more energy dense can be manufactured at scale.

Bodgerx said:

True, I got a bit carried away there. But, charging to 100% all the time will still degrade the LFP battery, just not at the same rate.

I think LFP will become the new norm for cars on the cheaper end of the spectrum, for sure. At least until something cheaper and more energy dense can be manufactured at scale.

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All batteries degrade over time it's unavoidable. Some faster than others, depending on chemistry, depth of discharge and recharge, and the number of rapid charges. That said, the car will still drive even with severe degradation . . . just not as far as it used to.

N2STY said:

NMC batteries support about 1,000 to 2,300 cycles, depending on conditions

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That's a huge difference, so what exactly are the desirable and undesirable conditions which cause this variance?
Also, is every recharge counted as a full cycle? If, for instance, I charge my Trophy LR from 40% to 65% does that count as a full cycle or is it only regarded as complete if I charge up to 80% or maybe 100%?

A full cycle is 0 to 100% in normal terms but 4x 25% or 5x 20% is also classed as a full cycle but is better for the battery as you don't go to low or to high

N2STY said:

A full cycle is 0 to 100% in normal terms but 4x 25% or 5x 20% is also classed as a full cycle but is better for the battery as you don't go to low or to high

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Interesting. Thanks @N2STY. At roughly 1 complete cycle a week I can reasonably hope for a battery life of 20 years or more so that'll do.

Definitely in the territory where batteries will out live an ICE engine, for sure.

jaykew said:

Interesting. Thanks @N2STY. At roughly 1 complete cycle a week I can reasonably hope for a battery life of 20 years or more so that'll do.

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I think them charge cycles are when a battery reaches 30% degradation so if all goes well you will still have 70% range left

Bodgerx said:

No it doesn’t

This is a misunderstanding from some posters on this forum.

If you look at the manual, both batteries have the same recommendations as far as balancing charging for the health of the battery.

Constantly charging to 100% will have a similar degradation effect to the LR. It’s not even more ‘tolerant’ of it.

The only reason MG took off the 80% restriction function is related to the fact it’s a bit more difficult to work out the SoC on LFP batteries, and going to 100% allows the BMS to get a better calibration.

Click to expand...

Not true, NMC batteries are on the way out now that the patents have expired (China ignores patents) as they are better in most motoring applications.

There is no negative effect from charging to 100% Tesla Recommends Charging Model 3 RWD's LFP Battery To 100%

Yet Tesla will not be using any LFP battery on there high end models it's all down to cost there saving there best batterys NMC (until a better option is made )for performance and distance
Tesla recommend 100% charge on LFP the same as MG for better range prediction and for the BMS that said LFP should last the 3000 cycles which is more than NMC but LFP keep below 90% with occasional balance charges could make 10000 cycles

N2STY said:

Yet Tesla will not be using any LFP battery on there high end models it's all down to cost there saving there best batterys NMC (until a better option is made )for performance and distance
Tesla recommend 100% charge on LFP the same as MG for better range prediction and for the BMS that said LFP should last the 3000 cycles which is more than NMC but LFP keep below 90% with occasional balance charges could make 10000 cycles

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They use the NMC for the energy density getting the best results for the performance models. Those results aren’t required for the rear wheel drive models. Tell you what though, it’s still a rocket ship.

DriverX said:

Not true, NMC batteries are on the way out now that the patents have expired (China ignores patents) as they are better in most motoring applications.

There is no negative effect from charging to 100% Tesla Recommends Charging Model 3 RWD's LFP Battery To 100%

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No idea what you are disagreeing with here