Charging 10%-100% every 3-6 months

From what I know is the worst thing you can do is charge it to 100% and leave it without driving for weeks

Rolfe said:

I think so. I'm planning another drive to Sussex in May, so I'll do a <10% to 100% charge again not long before I leave, to be belt and braces certain that the GOM is as accurate as it can be. I'm intending to head for Forton for my first charge, nearly 150 miles at motorway speeds, and I don't want any nasty surprises on the M6.

After that I hope to get to the NEC charging hub, though that will mean charging to about 85% at Forton, and going down close to 10%. I've got a good plan worked out, but I wouldn't feel comfortable with it if I couldn't reasonably trust the GOM.

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A newish Gridserve bank of chargers at Pease Pottage services at the bottom of the M23 or the Gridserve hub at Gatwick. No Tesla SCs around to save money with though. It's sunny in Sussex today and the rain has stopped for now!

Lovely, but as my second charge will be at NEC Birmingham if all goes to plan, from there I can't even get to Gatwick never mind Pease Pottage! I reckon the Ionitys at Cobham, and just stay long enough to get to Portslade with however much charge will enable me to get from there to Glyndebourne the following afternoon with enough in the battery so the Glyndebourne destination chargers will be able to take it to 100% and balance, so I'm set for the return journey.

I reckon I want to be on about 40-50% when I arrive at Glyndebourne, so I'll work back from that.

Rolfe said:

Lovely, but as my second charge will be at NEC Birmingham if all goes to plan, from there I can't even get to Gatwick never mind Pease Pottage! I reckon the Ionitys at Cobham, and just stay long enough to get to Portslade with however much charge will enable me to get from there to Glyndebourne the following afternoon with enough in the battery so the Glyndebourne destination chargers will be able to take it to 100% and balance, so I'm set for the return journey.

I reckon I want to be on about 40-50% when I arrive at Glyndebourne, so I'll work back from that.

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Definitely a long trip for you. I work in Portslade (well...once or twice a week since Covid days). Haven't used the chargers at Glyndebourne but did see them when my daughter did a Christmas school choir performance there in Dec 22.

Last time I went, Forton only had a couple of 50 kW units and I couldn't risk it. If there was a problem there, there's a long stretch of M6 after the service station before you get to the next junction, and then I'd have had to start scouting for a Booth's or something. Not worth the stress. So I came off north of Lancaster and charged at Greenlands Farm. Then to the Ionitys at Stafford, and Cherwell Valley.

I could have got to Glyndebourne on what I arrived with at Portslade, but I was doubtful about then getting all the way to 100% and balancing on the destination chargers as they're not very powerful. So I went looking for a charger the next morning in Portslade. The BP Pulse at M&S was out of order, but I got what I wanted at a 50 kW Blink charger by Victoria Park. And the destination chargers actually did pretty well, even though a Leaf showed up and plugged in to the other cable on my post, which was annoying as there were plenty free posts. So mission accomplished, and the car had a balance charge before the string of rapids on the way home.

Now, with Forton looking reliable enough to chance it, I can get a lot closer to Portslade for my third charge, and just play it by ear. If I'm running really late I can just grab enough to get me to Portslade and have another session on the Blink in the morning. But ideally I hope to stop long enough at Cobham so I'll still have 50% at Portslade and avoid that extra charge. Glyndebourne is only about 16 miles on from there.

I’ve had my car for a year and I wasn’t aware of the 10~100% BMS calibration charge until fairly recently. I wouldn’t have been able to do it anyway as I’ve had a faulty CCU for the last five months, so I’ve been unable to use my home AC charger. As that’s been fixed I ran the car down to 5% SOC this evening and here are my recommendations from my experience. DO NOT do this on an A road and most definitely not a motorway.

The car was at 17% when I went to pick my wife up, just three miles away on an A road. On the return journey the car was at 15% and the yellow warning triangle popped up and the message “Power limited - speed limited” appeared. The maximum I could go was 54mph with slow acceleration. Below 10% was even worse. 45mph down to 28mph quite rapidly. It didn’t matter how hard I pressed on the accelerator pedal. Fortunately there is a quiet B road near where I live, so I pootled about at 28mph until I got to 5% SOC.

It’s on the Zappi now and I’m guessing it will take between 8 ~ 9 hours to charge up to 100%.

I learned one important thing from this. Only let the car go below 15% if you’re driving in a built up area (20~30mph speed limit).

A word of comfort. Your car appears not to have had a normal balance charge at 100% for quite some time. What you experienced seems to be related to that. The car ends up not having much of a clue where the hell it is in the discharge curve, and can over-estimate remaining range. Then when it gets down to the steeper part of the curve below 10% it can see exactly where it is. At that point the car has a sudden "what the freaking hell?" moment and re-calibrates the SoC and the GOM to show the truth, much to the dismay of the driver.

I think you've really been significantly lower on charge than you realised, due to the lack of balance charges, and the car has flung itself into reduced power and even turtle mode at what seemed to be a much higher SoC than you'd have expected because of that. I do not think it will do this to you once it's had its regular balance charges.

There are several videos of people driving MG4s down to empty and they don't seem to do this. Presumably they'd had their usual schedule of balance charges. Bjorn Nyland drove one 15 miles round a car park to get it to die completely - admittedly that was perforce slow driving.

The LFP battery is reputedly even worse for this than the NMC, nevertheless mine is always absolutely on the nail when I've driven it low. I once overtook a car doing 80 mph at 5% charge. However I charge to 100% and balance once or twice (or sometimes three or four times) a week. The NMC only needs to do it every month according to the manual.

@Rolfe Yes, I’m sure not being able to balance charge for the last five months has resulted in what you describe Rolfe. It was rather disconcerting though and fortunately I wasn’t on my way back from Dundee or Perth and experienced this on a busy, main road. I just need to get the software patch (problem incurred after getting new CCU)now, so that I can do my regular charges to 80%.

It must have been quite scary. Maybe the lesson is that if you've had this problem, not to do the long charge until you've been able to do a couple of 100% balance charges first. Might help.

FiferMG4 said:

I’ve had my car for a year and I wasn’t aware of the 10~100% BMS calibration charge until fairly recently. I wouldn’t have been able to do it anyway as I’ve had a faulty CCU for the last five months, so I’ve been unable to use my home AC charger. As that’s been fixed I ran the car down to 5% SOC this evening and here are my recommendations from my experience. DO NOT do this on an A road and most definitely not a motorway.

The car was at 17% when I went to pick my wife up, just three miles away on an A road. On the return journey the car was at 15% and the yellow warning triangle popped up and the message “Power limited - speed limited” appeared. The maximum I could go was 54mph with slow acceleration. Below 10% was even worse. 45mph down to 28mph quite rapidly. It didn’t matter how hard I pressed on the accelerator pedal. Fortunately there is a quiet B road near where I live, so I pootled about at 28mph until I got to 5% SOC.

It’s on the Zappi now and I’m guessing it will take between 8 ~ 9 hours to charge up to 100%.

I learned one important thing from this. Only let the car go below 15% if you’re driving in a built up area (20~30mph speed limit).

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I took my Trophy down to 8 or 9% last week and had no 'power limited' messages. I deliberately floored the accelerator a couple of times and each time it showed 100% power and felt like it, picking up speed normally to 60+ mph (couldn't do much more than that round the lanes I was on). So I think @Rolfe is probably right about your inability to balance the battery recently having a negative effect on your car.

FiferMG4 said:

I’ve had my car for a year and I wasn’t aware of the 10~100% BMS calibration charge until fairly recently. I wouldn’t have been able to do it anyway as I’ve had a faulty CCU for the last five months, so I’ve been unable to use my home AC charger. As that’s been fixed I ran the car down to 5% SOC this evening and here are my recommendations from my experience. DO NOT do this on an A road and most definitely not a motorway.

The car was at 17% when I went to pick my wife up, just three miles away on an A road. On the return journey the car was at 15% and the yellow warning triangle popped up and the message “Power limited - speed limited” appeared. The maximum I could go was 54mph with slow acceleration. Below 10% was even worse. 45mph down to 28mph quite rapidly. It didn’t matter how hard I pressed on the accelerator pedal. Fortunately there is a quiet B road near where I live, so I pootled about at 28mph until I got to 5% SOC.

It’s on the Zappi now and I’m guessing it will take between 8 ~ 9 hours to charge up to 100%.

I learned one important thing from this. Only let the car go below 15% if you’re driving in a built up area (20~30mph speed limit).

Click to expand...

Hmmm haven’t noticed the described behavior until my phase 1 MG4 Trophy LR dropped below 10% last time. I was deliberately taking multiple detours to get my battery below 10%.

Acceleration became less, but Icould still easily reach 80km/h /50mph.

Weird

Thanks for the feedback guys. I’m glad to see this behaviour is not normal and that it would seem mine has been affected by the lack of balancing.

It’s not just the balancing per se, but the ability of the BMS to see ‘stable and reliable’ voltages at ALL states of charge that ensures its accuracy.
If you never balance properly at 100%, that obviously is going to make things much worse.
But it really helps the BMS to see stable states of charge below 25%.

@pecker and others - thanks for this thread. I really wasn't aware of the 10-100 recommendation, and wondered how we could do it, as there is at least 35 miles between chargers in our neck of the woods. so getting the sums wrong is fraught with danger.
As it happens, we're in Orkney for a short holiday, and there are just so many chargers here, we were happy to run the car down to single figures this afternoon.
Also great - we used no power at all on the ferry! And a final pleasure - we've already seen another black MG4 on the island. Just as well Goth Leo is on his lead tonight.

Did my first 100% balance charge today for around 6 months, although I've done some balance charges at 80%. Yesterday I left it on charge on the solar to 80% and let it balance, then without using it I plugged it back in (granny charger) and let the sunshine do its bit. It took 7.5 hours to complete and according to my smart plug consumed 16.1kWh of electricity. Even though it balanced at 80% yesterday it took around 45 minutes to balance and at the end the gom gave me an estimated range of 286 miles.