MG4 51kwh Battery Management System problems?

Hi,

Anybody having battery problems with their MG4? I've had no problems up until this last week, now suddenly the cars battery seems to drain at an insane rate. Last week my car dropped from 52% down t0 31% within 19 miles and an average of 2.5kwh efficiency (anyone else seem to think there is no rhyme or reason to this reading? However many things are switched off and however efficiently you drive, the number seems totally random.) and ave speed of 5mph. Today I charged the car to 83% and within 3 miles the car has lost 5% of its battery.

The car is generally slow charged between 50-80% at our local supermarket 7kw charger, today it was given a 50kw rapid charge (only it's 2nd rapid charge so far.) Upon plugging in the CCS cable the app was reporting that the chargeport and battery were too hot, but nothing was appearing on the dash or the infotainment system to back this up, so maybe an app glitch??

This car is my first EV so maybe my expectations are too high, but this is really looking like it is going to have to go in and get checked over.

sounds a bit worrying unless you are flooring it everywhere. maybe balance charge might help it a bit?

I've seen some say that since the App was updated recently, it always says the battery is too hot so perhaps you're seeing the same bug?

jon0881 said:

sounds a bit worrying unless you are flooring it everywhere. maybe balance charge might help it a bit?

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Sadly not, that would at least explain it and be fun too.

OJEastwood said:

I've seen some say that since the App was updated recently, it always says the battery is too hot so perhaps you're seeing the same bug?

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Thanks that could explain the app, I have just opened it up again (3 hours after finishing charge.) and apparently the battery and port are still too hot.

I've also noticed that I can no longer set the target charge.

This is likely to be the BMS losing track of the state of charge in the battery. LFP batteries are prone to this due to their flat discharge curve and I think the SR ZS has had similar reported. This is the real reason they tell you it is ok to charge to 100% as they need you to do it as often as possible.

Try charging to 100% a few times in a row and if this doesn't work then also try discharging it to below 10% before a 100% charge.

Found it:

Sudden SOC drop on my Mk2 ZS EV SR

MoDolph said:

This is likely to be the BMS losing track of the state of charge in the battery. LFP batteries are prone to this due to their flat discharge curve and I think the SR ZS has had similar reported. This is the real reason they tell you it is ok to charge to 100% as they need you to do it as often as possible.

Try charging to 100% a few times in a row and if this doesn't work then also try discharging it to below 10% before a 100% charge.

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Thanks I will give this a go. I don't have a home charge point and with the car not being supplied with a granny cable it only tends to get a couple of 3 hour charges at our local tesco each week to keep it at around 80%.

I think this is much more likely to be a BMS problem rather than an actual battery problem so I've amended your thread title.

gjdalk1 said:

Thanks I will give this a go. I don't have a home charge point and with the car not being supplied with a granny cable it only tends to get a couple of 3 hour charges at our local tesco each week to keep it at around 80%.

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It needs 100% regularly.

Have you ever done a full balance charge on the car? The reason that I ask is that it was not done on my car when it was PDI'd and it then caused lots of issues with charging etc. I'd suggest that you give the car a full balance charge as soon as possible - if you don't have access to a home charge point consider asking a friend to do it at their house.

BugEyed said:

Have you ever done a full balance charge on the car? The reason that I ask is that it was not done on my car when it was PDI'd and it then caused lots of issues with charging etc. I'd suggest that you give the car a full balance charge as soon as possible - if you don't have access to a home charge point consider asking a friend to do it at their house.

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Thanks, I've only done top ups so far, because of my charge point situation. Thankfully my parents are getting a mokka e and getting a charger point installed in a couple of weeks. So I'll have to ride it out for a week or 2 then get a balance charge there once installed.

Get it done ASAP. Can you borrow a granny charger and charge it overnight or at the weekend at your Parents?

Hi all, just a quick update on this car, it went into the MG dealer today to resolve the BMS and other snags, what can I say?

I come home from work, to find the car all shiny and gleaming, show room fresh, so I jump I'm the car and that's where the good news ended.

My battery had dropped from 70% to 40% even though the dealer is only 12 mls away. I had gained warning lights for the parking brake, traction control and dynamic stability control. My android auto which had the annoying pre-production watermark no longer has this message.... but that's only because it now won't launch at all. The 12v socket wasn't working and the rear window would only demist half the window and both are still exactly the same... so slightly peeved to say the least.

MoDolph said:

This is likely to be the BMS losing track of the state of charge in the battery. LFP batteries are prone to this due to their flat discharge curve and I think the SR ZS has had similar reported. This is the real reason they tell you it is ok to charge to 100% as they need you to do it as often as possible.

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Wouldn’t a shunt be used to track the state of charge?

thejaybeeok said:

Wouldn’t a shunt be used to track the state of charge?

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I'm more of a chemist than an electronics guy but I think a shunt allows something like coulomb counting? If so, manufacturers usually do implement that between charges but it still needs to be calibrated occasionally by using the raw voltage values as it is prone to drift.

thejaybeeok said:

Wouldn’t a shunt be used to track the state of charge?

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My understanding is alot of BMS systems for EVs use open circuit voltage with load profiling for SoC determination, hence the need to balance regularly on LFP