Charging 10%-100% every 3-6 months

[Rolfe]

The reason for the charge is so the BMS can tell the scope of the battery pack, so I would charge in one go, it's only every 6 months so it won't break the bank.

That's my feeling also. If I'm going to take the trouble to run the car down to <10% then I want the subsequent charge to do the business, not to fudge it and hope for the best. I've managed to do it twice with a granny charger, simply by choosing a day when I knew I wasn't going to be needing the car and charging for getting on for 26 hours non-stop.

With a home charger it's only going to be 8-9 hours I think, so you could do it over a single night without worrying about the car not being used for a day. And in the grand scheme of things, it's pocket change.

 

[Ian Key]

The reason for the charge is so the BMS can tell the scope of the battery pack, so I would charge in one go, it's only every 6 months so it won't break the bank.

With a home charger it's only going to be 8-9 hours I think, so you could do it over a single night without worrying about the car not being used for a day. And in the grand scheme of things, it's pocket change.

Yes, it won't break the bank but it would still be useful to know.
What would happen if you had a power-cut for a short time during the night? Does that mean you have to run it down to 10% and try again?
What about those on an intelligent tariff which splits the charging? Do they have to start again too?

 

[MGFour]

Would be interesting to know, but I don't think it would be anything to worry about if you don't achieve it in one go, the car would surely make sure you know it needs doing if any negative affect.

 

[Rolfe]

I'm inclined to think it would probably be all right if the car wasn't driven during the charge, but I don't know for sure. I think the way the car would "make sure you know its needs doing" would be to drop the % charge reading and the GOM range precipitiously as you're around 10% charge, so maybe not something to risk.

Happened to this guy when he was given a press car for a week. The car had probably been repeatedly rapid charged without any thought of balancing, and it just about landed him in it. Now he's saying on all his videos that the GOM is really unreliable and it's "dangerous" to drive the car below 20% charge.



We all know that isn't true, because we balance our batteries. But that's how the car lets you know you haven't been doing it enough.

 

[tsedge]

Yes, it won't break the bank but it would still be useful to know.
What would happen if you had a power-cut for a short time during the night? Does that mean you have to run it down to 10% and try again?
What about those on an intelligent tariff which splits the charging? Do they have to start again too?

What reasons do you have for supposing that it has to be a continuous 10-100% charge?

The reason I ask is my understanding of these systems is that they are constantly sampling and the designers know people will not follow the rules reliably.

(Actually I am good example, I have never been down to 10%, 16% is my minimum so far).

 

[Ian Key]

What reasons do you have for supposing that it has to be a continuous 10-100% charge?

The reason I ask is my understanding of these systems is that they are constantly sampling and the designers know people will not follow the rules reliably.

(Actually I am good example, I have never been down to 10%, 16% is my minimum so far).

I have no reason for believing one way or the other. I was replying to the other comments ?

I have emailed our friendly MG customer services and asked the question and will post their reply as and when I get one.

 

[MG4ORR]

Where in the manual does it state charge from <10% to 100% every 3 to 6 months to carry out battery cell equalisation?

 

[siteguru]

Page 295:

 

[elias]

My car is already over 6 months old and I've never discharged it bellow 30%. I've only done charges to 100% every 2-4 weeks to allow for the normal cell balancing to run, but nothing else.

Thank you all for this thread, otherwise I don't know how long it would have taken me to find that warning in the manual.

TODO: Read the full manual.

 

[Matt x power]

Surely that contradicts the NMC maintenance charging Which is all over the internet

 

[MSvirus]

Page 295:

View attachment 24258

Are we sure this is for NMC, or is this for LFP (as I suspect)?

 

[fnegroni]

Surely that contradicts the NMC maintenance charging Which is all over the internet

Not all NMC batteries are the same
Not all BMS are the same
The Internet is full of people telling others how to maintain their batteries but don’t even own an EV and have never experienced a sudden drop below 30%
Many have Tesla s and will only do what the Tesla manual tells them to do and think all other cars are the same
some manuals are wrong too ?

The benefit of occasionally dip below 10% is related to the BMS and the manufacturer must know a thing or two that we don’t.

 

[tsedge]

Page 295:

View attachment 24258

As others have said, this must be LFP pack guidance - perhaps they are covering both bases in one sentence but it doesn't make sense to do both with NMC.

I have had my car a year, never got down to 10%, the battery is fine.

 

[tsedge]

While I can understand why going down to 10% occasionally would be good for the battery, I am wondering whether to keep bothering following all this guidance.

It feels like some kind of treasure hunt, decoding the clues to try to work out where the gold is buried for a long battery life.

So many average people who are not interested in EVs are simply never going to read the manual or care and won't follow the guidance - so the cars will have to cope somehow anyway.

Also the pack is warranted to stay above 70% health, which is actually enough range for me anyway, so why should I worry?

With the recent CCU issue that forced me to DC charge only to 90%+ regularly for several months with no balancing, the car has been just fine with zero noticeable change.

 

[Adam C]

While I can understand why going down to 10% occasionally would be good for the battery, I am wondering whether to keep bothering following all this guidance.

It feels like some kind of treasure hunt, decoding the clues to try to work out where the gold is buried for a long battery life.

So many average people who are not interested in EVs are simply never going to read the manual or care and won't follow the guidance - so the cars will have to cope somehow anyway.

Also the pack is warranted to stay above 70% health, which is actually enough range for me anyway, so why should I worry?

With the recent CCU issue that forced me to DC charge only to 90%+ regularly for several months with no balancing, the car has been just fine with zero noticeable change.

It all confuses the life out of me but in my defence I’ve only had my MG4 a month now & have been using public chargers ( 50kW ) because my home charger won’t be installed until April/May.

Before I picked the car up the dealer did tell me if I can it’s best to keep the car between 20-80% but if I plan a long trip then it’s ok to go to 100%. He never told me anything else, didn’t mention balancing etc.

Only this morning my car was on 21%, I used a public charger & just topped it up to 60% which for the mileage I do will be fine for a good while.

I’ve talked to a neighbour of mine, he has a MG ZS EV, ( nearly 7000 miles ) he can’t have a home charger due to no garage/driveway so he only uses public chargers. I said to him about keeping it at 80%, he just smiled & said he sticks it on a fast charger when he & wife do shopping & most of time charges it to 90-100% whatever the battery % is on at the time & he’s had no issues.

So I think like you said, for the vast majority of EV owners & future owners, they will plug in when needed & just go

 

[Kevin Smith]

We have various tariff slots and only a granny charger but when I did the maths on what does the whole charge cost across 24 hours I decided that I shouldn’t sweat the small stuff, just reach in the pocket and pay the £15 and think what it would have cost at the petrol pump!

 

[pecker]

I think this really needs clarifying by MG for the two different battery types.

VW recommended keeping the battery between 20-80% for the ID range.

Confused now

 

[Kevin Smith]

I agree. The manual just describes type 1 &2 batteries and it took some digging to find out the 51 kWh battery is LFP. These tolerate deeper cycles better and like charging fully. It would be so easy to put a battery card into each car with details of management recommendations or just a QR code sticker in the charging hatch leading to details online!

 

[Adam C]

I think this really needs clarifying by MG for the two different battery types.

VW recommended keeping the battery between 20-80% for the ID range.

Confused now

I posted this before, it all confuses the hell out of me lol

My dealer told me before I picked my car up ( Trophy Long Range ) it is best to keep it between 20-80% but if I plan on doing a long journey just charge it to 100%. Also he never mentioned anything about battery balancing etc

Now I’ve watched quite a few YouTube videos & often one person says A, another B & the next person C so it really can be a minefield to work around

So my thinking is now I’ll just drive it & stop watching loads of different videos

If I’m out & the battery is nearing 20% I’m not going to panic & rush to a charger so it doesn’t drop below, I’m sure it will be ok if it drops to 10-15%. Of course I’m not going to be stupid & regularly let it get down to 5% & charge it every time to 100% but I’m not going to give myself a headache trying to run it to the letter especially where again there’s so much different advice about it all.

What I did notice once when charging ( I’ll post picture ) is on the charging screen 0-80% it says Battery Health Mode

Then a blue line, then it says Long Journey Mode which is obviously 80-100-% which I guess is one reason the dealer told me that ideally it is best to keep it between 20-80%

Yes all very confusing but I still have no regrets about grabbing an MG4. Like anything new, it’s just getting used to it all

 

[siteguru]

NMC battery cells have a fairly linear voltage curve, so it's easy for the battery management system (BMS) to calculate how much charge is left. However NMC doesn't like (that much) being very high or very low state of charge (SoC) for an extended period, as it causes chemical reactions which can degrade the cell performance. That's why 20-80% for normal use is suggested. However there's nothing stopping you going lower than 20% when needed, or charging to 100% when you know you've got a longer journey the following day. Plus a balance charge at 100% is recommended monthly.

The LFP battery cell in the SE SR has a flat voltage curve ... the voltage drops a little as you come down from 100% SoC and then goes across fairly flat until close to 0% SoC whereupon the voltage drops off. This makes it harder for the BMS to determine SoC, and is why a) 100% charge is OK for LFP, and b) weekly balancing is recommended.

But as with everything, these are just guidance and recommendations. If you're not keeping the car for more than 7 years (the battery warranty period) then it doesn't really matter.