80% or 100%

[Museruk]

Surely if leaving the LR NMC battery at 100% charge for a day or slightly longer is going to potentially cause degradation of the battery, then it is an indirect and non-obvious statement in the MG4 manual, since they start the precaution with 'When using the vehicle on a daily basis...
They do not mention the potential issue if the car is not used with 100% charge for a few days!

 

[tsedge]

Surely if leaving the LR NMC battery at 100% charge for a day or slightly longer is going to potentially cause degradation of the battery, then it is an indirect and non-obvious statement in the MG4 manual, since they start the precaution with 'When using the vehicle on a daily basis...
They do not mention the potential issue if the car is not used with 100% charge for a few days!

It could be clearer, yes.

 

[Museruk]

It makes me wonder if this rule of frequently charging to 100% when using the EV every day is purely to ensure that the MG battery management system (BMS) is kept as accurate as possible?
Problem with getting into the MG recommended habit of charging every night to 100% (assuming this is possible with the limited low cost period of overnight charging) is that I can see that if you were to go on holiday for a week or longer (leaving the car at home), then it would be easy to forget to leave the battery in the recommended 50% to 80% charge range to avoid potential battery damage!

 

[Rolfe]

As far as I know, it's the LFP battery that needs to go up to 100% every time to keep the BMS accurate. The NMC, allegedly, can manage repeated 20% to 80% cycles and only needs to balance at 100% once a month. The NMC will also balance to some extent at 80% so long as it's on an AC charger and allowed to sit on the charger once it has got to the target 80%.

 

[Deleted member 10041]

NMC battery prefers 20-80% however there is no major issue with charging higher and running lower when the trip dictates.
Issues can crop up if you charge to 100% then leave it for a prolonged period.
There was a member on here who was probably amongst the most experienced EV owners I've ever chatted to did huge annual mileage and charged to 100% everyday In life, he changed his car every year due to his excessive mileage but he stated there was no real degradation in his batteries.

 

[Rolfe]

I suppose his cars never sat at 100% for any length of time if he was doing such a huge mileage.

The difference I see between the two technologies is that NMC is less tolerant of sitting at 100%, but is happy to go up and down between 20% and 80% repeatedly. The LFP seems not to like that, and prefers to go up to 100% and balance at every charge, but on the other hand it's more tolerant of sitting at 100%.

Obviously if you're doing a big mileage every day you'll charge an NMC to 100% every day, because you won't be stressing it by making it sit at that SoC for more than a handful of hours at a time.

 

[Museruk]

It follows then that this confusion may be simply to the fact that MG have decided (presumably to keep documentation update costs down) to have a common 'one manual' for all battery / model variants of the MG4 and the statement I picked out may be referring to the SE LFP battery - thus ignoring the higher mileage NMC battery requirement?

 

[bowfer]

It makes me wonder if this rule of frequently charging to 100% when using the EV every day is purely to ensure that the MG battery management system (BMS) is kept as accurate as possible?
Problem with getting into the MG recommended habit of charging every night to 100% (assuming this is possible with the limited low cost period of overnight charging) is that I can see that if you were to go on holiday for a week or longer (leaving the car at home), then it would be easy to forget to leave the battery in the recommended 50% to 80% charge range to avoid potential battery damage!

Of course it’s possible to charge to 100% using cheap periods.
I’m 6 hours cheap power, my charger is 7KWh (or some might say slightly less for losses etc)
That’s 42KWh going into a 58Kwh battery.
I’d have to be quite low on charge to fail to reach 100% on that.

 

[tsedge]

It makes me wonder if this rule of frequently charging to 100% when using the EV every day is purely to ensure that the MG battery management system (BMS) is kept as accurate as possible?
Problem with getting into the MG recommended habit of charging every night to 100% (assuming this is possible with the limited low cost period of overnight charging) is that I can see that if you were to go on holiday for a week or longer (leaving the car at home), then it would be easy to forget to leave the battery in the recommended 50% to 80% charge range to avoid potential battery damage!

With the LFP battery, the MG recommendation is a 100% charge once a week, not every time you charge it. It is fine being charged to other levels so long as once a week you do a 100% charge.

For NMC it recommends 100% once a month, but no problem doing it more often than that as needed for long distance.

Fears about the effects of overcharging on range and degradation are often overblown, so it is not something I worry about, I just use the car as I need to.

If you are keeping it for 10 years or doing a taxi mileage, these things will make a difference, but otherwise life is too short.

 

[Museruk]

With the LFP battery, the MG recommendation is a 100% charge once a week, not every time you charge it. It is fine being charged to other levels so long as once a week you do a 100% charge.

For NMC it recommends 100% once a month, but no problem doing it more often than that as needed for long distance.

Fears about the effects of overcharging on range and degradation are often overblown, so it is not something I worry about, I just use the car as I need to.

If you are keeping it for 10 years or doing a taxi mileage, these things will make a difference, but otherwise life is too short.

I agree wholeheartedly!
Enough said!

 

[Rolfe]

It follows then that this confusion may be simply to the fact that MG have decided (presumably to keep documentation update costs down) to have a common 'one manual' for all battery / model variants of the MG4 and the statement I picked out may be referring to the SE LFP battery - thus ignoring the higher mileage NMC battery requirement?

That's what I was thinking. What you quoted sounded like a bit of a mish-mash of the two battery types. They really ought to be more clear about it.

At first, I believe, you could set the 80% charging limit on the app for all cars. Then by the time I got my car, although it looked as if you could do that, in practice the SR ignored the limit and went right on to 100% regardless. Confused the life out of me, because I'd been reading so much about charging to 80% (although my dealer said no, charge to 100%). At the last revision the ability to set a charging limit disappeared entirely for the SR.

MG are clearly pushing SR owners to charge to 100% whenever the car is left on its own to charge.

With the LFP battery, the MG recommendation is a 100% charge once a week, not every time you charge it. It is fine being charged to other levels so long as once a week you do a 100% charge.

For NMC it recommends 100% once a month, but no problem doing it more often than that as needed for long distance.

Fears about the effects of overcharging on range and degradation are often overblown, so it is not something I worry about, I just use the car as I need to.

If you are keeping it for 10 years or doing a taxi mileage, these things will make a difference, but otherwise life is too short.

The way it seems to work with the LFP is that you can't set the app to cut its charge short. Unless you physically intervene, it will get to 100% and balance. If you're on an AC charger there's really no point in doing anything else unless you need to get on your way sooner.

If you're on a DC charger you're probably going to stop the charge short of 100% for all the usual reasons anyway. (The day I left mine on a DC charger because reasons, it actually stopped by itself at 98%.)

So there are going to be occasions when, even with the LFP, you're not going to charge to 100%. Either you're on a DC charger, or you need to interrupt an AC charge to get going. If you're doing much of that, you have to remember to let the car get to 100% and balance at least once a week. But if you let it do its own thing, it will go to 100% and balance every time you charge.

 

[Vingnut]

LFP batteries does not need the 100% charge, they are perfectly happy to sit at 80% soc.
The problem is the discharge voltage curve is very flat and drops only at the very end (make it very hard to read their soc and calculate range). So it's realy the cars BMS that need the 100% charging once a week to determine correct soc. Happily LFP batteries have very low degradation so the 100% is not realy a problem.

The LR batteries does have a fairly even voltage discharge curve that make it easy to determine their soc.

 

[Rolfe]

Yes, I include having a GOM that isn't a random number generator as a reason the batteries "need" that charge. I think we saw one that was in trouble in that respect in another thread. It was a second-hand car that was presenting with very strange range estimates. Unfortunately the first thing anyone said in the thread was, oh that's probably a battery that's been damaged because it's been taken to 100% too often. On further investigation it seemed that the opposite was the problem - the battery hadn't been taken to 100% often enough.

 

[Lovemyev]

Here is a recent, fantastic video from an expert on the subject of EV battery health / SOC for holidays etc.

 

[Rolfe]

That's absolutely excellent. He explains it so clearly.

 

[Lovemyev]

That's absolutely excellent. He explains it so clearly.

This guy is a real battery guru and knows his stuff !.

 

[Rolfe]

I've heard so many contradictory and confusing statements that it's taken me some time to work out the real situation. I've been lectured to by people insisting that even LFP batteries are harmed by being taken to 100% and should be run between 20% and 80%. Then they go on to say that really, it's better to run between 40% and 60% whenever possible!

I've heard people lay down the law as if LFP batteries didn't even exist. I've heard people talk as if these batteries, particularly the NMC ones, are so fragile that if you don't drive them off the minute the reach 100% they'll probably die in a couple of years

The knee-jerk reaction to the member who posted about the battery in his second-hand SR which was reporting strange figures, saying that the battery had probably been irreparably damaged by being taken to 100% too often, was typical, but probably just the consequence of the guy that posted that having read so much of this misleading stuff. The car was barely a year old and had only done 8,000 miles! Even if it had been an NMC battery, it shouldn't have degraded by then! But in fact the post was suggesting that the battery had been damaged in a very short time by being treated exactly as MG tell us to treat the LFP batteries. In reality it's likely the GOM was misreporting because the previous owner had either tried to treat it like an NMC, or had been using DC chargers a great deal and never allowing the cells to balance that way.

What I liked about that video was the realism, telling even NMC owners how much leeway they have and debunking the idea that you have to be so so rigorous with these things or else they'll be ruined.

What I didn't quite catch was whether his warning not to do repeated short cycles at the top of the battery applies only to the NMC or whether he'd also advise against doing that with the LFP. I tend to leave my car alone until it's gone down below 50% or so, or until I need most of the range the next day, and then charge to full. But it might suit me to do the short cycles thing, so I wonder if it's OK in the LFP.

 

[Vingnut]

Just one correction Rolfe, most of the battery degradation is done the first year (months) and from then it slows right down, that is one of the reasons for the car companys to "hide" a bit of battery capacity on top soc. Often when we se 100% soc in reality it's 96/97% when we buy the car, and this is tapering down as the car is getting older (Tesla for one "hide" initial degradation this way).

The other reasons are to protect the battery (keeping it from reaching true 100% soc reduces charging cykles) and to let us have regen from closer to stated 100% soc.

 

[tsedge]

Just one correction Rolfe, most of the battery degradation is done the first year and from then it slows right down, that is one of the reasons for the car companys to "hide" a bit of battery capacity on top soc. Often when we se 100% soc in reality it's 96/97% when we buy the car, and this is tapering down as the car is getting older (Tesla for one "hide" initial degradation this way).

The other reasons are to protect the battery (keeping it from reaching true 100% soc reduces charging cykles) and to let us have regen from closer to stated 100% soc.

Yes, the other thing that is often forgotten is that the NMC battery has a top and bottom buffer in it which protects the battery and can limit the signs of degredation (by reducing the buffer as the battery ages), at least until the buffer is depleted.

 

[Vingnut]

Wow, watched the video now. From now one this video is the way to explain tis, very very clear and nuanced information about LFP and NMC batteries.

Especially the part of shallow charging is something to be aware off as it feels a bit against my nature to not top up the car to 80% when possible even it's at 70% (the urge to have range ready whenever when very seldom realy needing it).