@MG expert Charging 80% useful?

[Johnberg51]

I've always wondered myself how much is the top protection buffer of the MG HV battery.
After I did some research myself and did read that the battery is having 18 modules each with 6 serial blocks of 110A.
So 108 blocks serial connected.
On the infoscreen I saw that the HV battery voltage is about 452V when 100% charged.
This means every seperate cell is having a voltage of 452 : 108 = 4,2 V
I did hope so much that this would have been 4,1 V.
It is a physical property that a LiOn cell is 4,2V when 100% charged.
My conclusion: the MG battery does not have a top protection buffer!
Everybody knows what the lifetime of an Ebike battery is, which is also charged to 100% without protection buffer!

I don’t use my car much, maybe a 100 miles a week.
I think it is very bad for the battery to charge 100% and then not use it for a day or so.
So now I think to do the following:
Charge 4 times to 80%
After 4 times proceed one fully charge to 100%, so MG can do equalization (balancing) of the cells.
Of course also charge to 100% when making a long trip at the same day.

Charging to 80% is easy, just use a granny set to 10A which result in 4,7%/hour. From 25 to 80% will take about 11-12 hours.
After I end the charging by unlocking the doors and remove cables.
Maybe you also could use a time switch, but I know that electronics are not happy with abrupt cutting off the main power.

I am very interesting in your opinion about this, maybe I am too much carefull.
Or maybe, I hope so, MG is having an other kind of battery protection.

I have attached a screenshot of a Youtube from Thailand.

 

[Kithmo]

Your conclusion is only based on your one assumption of "It is a physical property that a LiOn cell is 4,2V when 100% charged", it may be that the MG has a slightly higher cell voltage and is in fact protecting the battery.

 

[Johnberg51]

Your conclusion is only based on your one assumption of "It is a physical property that a LiOn cell is 4,2V when 100% charged", it may be that the MG has a slightly higher cell voltage and is in fact protecting the battery.

As far as I know all Lion cells are having the same properties.

 

[lee graham]

I believe the eZS has a 45kWh battery with 42.5kWh usable.

 

[Johnberg51]

Yes, I know but I think the difference is most for bottom protection.
Too much discharging even harms the battery more.

 

[KasEV]

@Johnberg51,
Thanks for your contribution.
I think your assessment of the voltage is correct but I do disagree with you conclusions. What one looks at when assessing battery buffers is the estimated rates of charge and discharge, the real life data of charge and discharge rates and the effectiveness of the BMS. One should approach it from kWh at time indicator shows 100 and kWh at time indicator says 0.
That is how it is done.
You are measuring one physical property of the battery and making conclusions about a different physical function.
To make things simple I will explain with an example.
Take a river with walled reinforced banks as the battery.
The width of your river is now fixed that is from one bank to the other. This is your voltage. The river has other two properties.... how deep and how fast does it flow. That is you rate of charge and discharge you can not make conclusions on these by measuring only the width of the river.
Now imagine on top of this there is a dam that controls the amount of water coming into the river. This is your BMS.
Now what are your conclusions ...... well you are trying to prove that because you know how wide a river is you know everything else about the river how much water it will discharge etc without taking into consideration all the other factors.
I hope you get the issue with this simple explanation.
The Voltage may be fixed but that is not the issue here.
You are absolutely right about charging to 80%. I manage my battery in a similar manner.
I am however told that in real life terms unless one fully discharges and fully charges with a rapid charger every single time then the rate of battery degradation is not different with daily slow top up charging unless one plans to keep the same battery for over 15-20 yrs.

 

[Johnberg51]

Wow, that’s a complete other view.
I read that the older Nissan EV’s had a build in option to charge to 80%.
The newer models don’t have this anymore, because the charging is native limited to 4,1V per cel, which means about 90% charged.
The 4,2 V from the MG is a hard fact and means 100% fully charged

 

[Frank]

come on guys, did you do this stupid shit with your petrol or diesel cars. What a lot of faffing around worrying about your battery. Just charge it every day if you have a home charger, (that is what it is for), its just a car, keep the tank full because its easy to do with a home charger and if there is ANY problem with the battery just pass it on to MG to fix.

I did not buy an EV to have to worry about the battery, as it is there is many other things that can go wrong but as it has a 7yr warranty I don't even worry about it one little bit. However in saying that my nearest MG Garage is 89 miles away so it is a pain in the backside to get them to look at anything. My heater blower has just started acting up in that when you try to go above 3 bars it just cuts out and initially I thought it was a fuse but no, when you turn the HVAC off and then back on it works perfectly until you try to above 3 bars again, so it is NOT a fuse but some other (probably software) problem. It is due its first service in Nov so I have asked them to look at the heater problem then.

Unless you are keeping the car long term past the warranty I would not even consider in any shape or form maintain some made up charging regime which is NOT even proven to be any benefit, all the inconvenience is just baffling to me, its a car and you probably will change it in 4 years, just enjoy it for what it is.

Regards

Frank

 

[Johnberg51]

If you make many miles every day, I should say yes, load it every day to 100%.
But in my case it sometimes happens that I don’t use the car for one or two days.
It would not be good if you made a fully charge before then.
I always use a car for more then 10 years and it would be fine to have a little bit battery power over (80% or so) by that time.
I think one or two charges a week is enough for me, so what do we talk about

 

[Frank]

Everyone to their own, I might only do 10 miles or less a day but I still put it on charge, I am confident that the BMS will maintain the battery health and if it doesn't then MG take the risk.

I do accept however if one is keeping the car for about 3 years past the warranty then there could be a case for having a charging regime but if MG themselves don't tell to do so then why bother, that is what the BMS is for.

The other thing is that (unless I am wrong) even if the battery loses some of its capacity it only affects the range available as my understanding is that car will still drive the same (performance etc etc) its just that it will only travel less on a charge.

Regards

Frank

 

[Paulie68]

come on guys, did you do this stupid sh*t with your petrol or diesel cars. What a lot of faffing around worrying about your battery. Just charge it every day if you have a home charger, (that is what it is for), its just a car, keep the tank full because its easy to do with a home charger and if there is ANY problem with the battery just pass it on to MG to fix.

I did not buy an EV to have to worry about the battery, as it is there is many other things that can go wrong but as it has a 7yr warranty I don't even worry about it one little bit. However in saying that my nearest MG Garage is 89 miles away so it is a pain in the backside to get them to look at anything. My heater blower has just started acting up in that when you try to go above 3 bars it just cuts out and initially I thought it was a fuse but no, when you turn the HVAC off and then back on it works perfectly until you try to above 3 bars again, so it is NOT a fuse but some other (probably software) problem. It is due its first service in Nov so I have asked them to look at the heater problem then.

Unless you are keeping the car long term past the warranty I would not even consider in any shape or form maintain some made up charging regime which is NOT even proven to be any benefit, all the inconvenience is just baffling to me, its a car and you probably will change it in 4 years, just enjoy it for what it is.

Regards

Frank

You are quite correct Frank, that it doesn't matter one jot to those of us selling the car before 7 years old. For very long term owners, and subsequent owners of the car in it's older years, it will matter much more.

Limiting charge to 80% is definitely not made up and not proven! It is an absolutely proven scientific fact that keeping well away from the top and bottom of the voltage limits of a lithium based cell will increase it's cycle life dramatically! 20% to 80% will see a much. much, longer battery life to 80% capacity than ordinary layman use of just "filling it up" at every opportunity. I'd particularly not want to buy your car when it's older having suffered from your "lead acid" style charging regime lol!!

Ironically, as we don't have the ability on the car to limit charging to 80%, MG do actually recommend only charging to 80% as often as possible and not leaving the car at 100% for any length of time. It's hidden away in the FAQ's on the website!

 

[Paulie68]

Everyone to their own, I might only do 10 miles or less a day but I still put it on charge, I am confident that the BMS will maintain the battery health and if it doesn't then MG take the risk.

I do accept however if one is keeping the car for about 3 years past the warranty then there could be a case for having a charging regime but if MG themselves don't tell to do so then why bother, that is what the BMS is for.

The other thing is that (unless I am wrong) even if the battery loses some of its capacity it only affects the range available as my understanding is that car will still drive the same (performance etc etc) its just that it will only travel less on a charge.

Regards

Frank

Yep, just a lower range from battery capacity reduction, car will be just fine in all other regards.

 

[Johnberg51]

I opened this topic for two main questions:

Could you have some profit if you intend to use the car for many years, if you charge to 80%?

Could it harm the BMS and battery if you manual cut off at 80%?

 

[Paulie68]

I opened this topic for two main questions:

Could you have some profit if you intend to use the car for many years, if you charge to 80%?

Could it harm the BMS and battery if you manual cut off at 80%?

Charging to 80% will definitely prolong the life of the battery, this is a fact. Unplugging the charger at 80% will definitely not damage your car at all.

If you have a smart charger that you can set to turn off after a given amount of time or current use, this is best. Other wise turning the charger off by unplugging the car won't harm your charger either. Cutting the circuit power to a charger via a timer on the circuit itself regularly can stress the charger components and might shorten it's life a little, but probably isn't a big deal except over the very long term.

 

[Frank]

I must have a look at the FAQ's, thanks.

 

[Paulie68]

I must have a look at the FAQ's, thanks.

Here you go:

Electric Life | MG Motor UK

Venture behind the wheel with our MG blog to view a whole host of articles written by experts. Learn about electric cars, top tech and more here.

mg.co.uk

Recommended 20% to 80% for best health of the battery, but ironic as the car provides no way to set these parameters at all!!

In your case Frank, I would try not to keep charging to full after every few mile trip as you say you do now, that is about the worst thing you can do to a lithium battery.

 

[Frank]

Going by that, I should indeed not charge it every night, thanks for the information.

Regards

Frank

 

[Noraf142]

Just remember that it does need to be fully charged regularly, for an equalization charge? to be done.

 

[Frank]

Thanks all, I have just decided I don't care enough about the battery life to worry about a charging regime, I will now just continue with my plug it in every night as I have done for the last 8 months I can't be bothered (as whotsername says) because one day when I need it the most I will have to travel off to Glasgow or Edinburgh when not expecting it so at least this way I am always fully charged "ready to go".

Frank

 

[Paulie68]

Thanks all, I have just decided I don't care enough about the battery life to worry about a charging regime, I will now just continue with my plug it in every night as I have done for the last 8 months I can't be bothered (as whotsername says) because one day when I need it the most I will have to travel off to Glasgow or Edinburgh when not expecting it so at least this way I am always fully charged "ready to go".

Frank

Fair enough, how long are you keeping the car for? It'll be very interesting to see how robust the current batteries are and how they hold up capacity wise with your usage pattern.