Battery balancing

[Cliff Mitchell]

Be careful, it may not have actually completed the balancing process.... The car will only balance for (we think) 10 hours maximum at a time.
If you have not ever balanced, it may take longer than the 10 hours to actually finish the balance.

I would suggest to be on the safe side, that after doing a few miles in it, you put it on AC charge again and let it go through the balance process again.
I have a little cctv camera in the front window that I can use to see when mine starts the balance and it completes, it's the only way I actually know what it is up to!
(I fully AC charge 3-4 times a week, so mine never needs to balancing for much more than a couple of hours anyway)

I was told earlier that the MG badge would glow while balancing and turn off when it is finished. From what you are saying that may not be the case?

 

[Cliff Mitchell]

The predicted range drops by about 15miles if only the fan is used (on cold with no aircon or heating). Does the fan also use the HV battery?

That seems to be the case, which is a bit silly. One would think you could isolate the fan from the AC. I use the fan a fair bit to demist the windscreen without the need for the AC.

 

[Coulomb]

That seems to be the case, which is a bit silly. One would think you could isolate the fan from the AC.

Yes. It seems to be laziness on the part of the firmware: just check the fan switch, oh, it's on, must be using air con or heat. Sheesh. There is about a 20:1 difference in power drawn by the compressor or heater versus the fan.

 

[JodyS21]

I was told earlier that the MG badge would glow while balancing and turn off when it is finished. From what you are saying that may not be the case?

That is correct the MG badge is either solid lit or pulses dependant on charging or balancing, it then goes out when it isn't doing either.
But, as I said it will only balance for a maximum amount of time per "charging" session, 10 hours I think it is. Dependant on how far out of balance it is, it may take more than 10 hours to get it back to a fully balanced state.
Normally it isn't a problem if you're fully charging and balancing regularly, in my case fully charging several times a week my balancing takes around a couple of hours.

This has been part of the problem with people getting their batteries back to full health after having the bad bms, some of them need literally hundreds of hours of balancing, but you can only get a maximum of 10 hours per charging session. So instead of just leaving their cars constantly plugged in & balancing to get it sorted out ASAP; after getting the max balance from the charge session, they have to use some of the battery up before they can then put it back on charge again to get another max balance session.

 

[jamesie]

Jody, are you on the most up to date BMS?

I am on the original (456v full charge and balance). Had a Zappi installed recently which allows me to monitor some basic info when charging. The balance part is done at around 2.5 kw and lasts between 15 and 20 minutes.

Have MG changed the balancing algorithm to run at a lower power and subsequently for longer?

 

[JodyS21]

Jody, are you on the most up to date BMS?

I am on the original (456v full charge and balance). Had a Zappi installed recently which allows me to monitor some basic info when charging. The balance part is done at around 2.5 kwH and lasts between 15 and 20 minutes.

Have MG changed the balancing algorithm to run at a lower power and subsequently for longer?

I'm on the Jan 2021 BMS.
I have the Ohme charger which very disappointingly doesn't give me data on how much power it is pulling etc.
I've never managed to see on my smart meter display what power it pulls on balance, but from what a few others have said, I thought it was just a few hundred Watts it pulled during balancing. People have also said that the power goes down from 7kW to something like 2.5kW when it's getting near full charge e.g. say between 95-100%. Are you sure it's not that part of the charge you're seeing at 2.5khw for 15-20mines, that'd make more sense?

I'm just going to check back on my cctv to see how long my last balance took (remember I charge to 100% most charges 3-4 times a week)...
edit. I've looked and very annoyingly as it gets light early in the mornings now, I can't see the MG light on my cctv to tell when it goes out.

Here's some historic data I recorded when charging to 100% (2-3 hours balancing):

 

[jamesie]

Mine cranks down to 3.5 kw at around 95% charge and then completes the balance at 2.5 kw. Unfortunately the Zappi app isn't the greatest at looking at historical charging data.

Will do a full charge in the next few days and watch it "live" so to speak.

 

[Jake]

Jody, are you on the most up to date BMS?

I am on the original (456v full charge and balance). Had a Zappi installed recently which allows me to monitor some basic info when charging. The balance part is done at around 2.5 kw and lasts between 15 and 20 minutes.

Have MG changed the balancing algorithm to run at a lower power and subsequently for longer?

Likewise. Mine charges to 456v and balance lasts around 15-20 mins.

 

[Lovemyev]

Mine cranks down to 3.5 kw at around 95% charge and then completes the balance at 2.5 kw. Unfortunately the Zappi app isn't the greatest at looking at historical charging data.

Will do a full charge in the next few days and watch it "live" so to speak.

@Cliff Mitchell .
I have kept a pretty good eye on my home energy meter over a number of charge / balance processes.
How sad is that !.
And it reports in the following manner.
From the onset of charge commencing, from a fairly low SOC - the energy meter will briefly report a draw of 3.5 kw's then will quickly jump straight up to just above 7.1 kw's.
It will pull 7.1 ish kw's until the SOC reaches around the 97 - 98% mark.
The MG badge on the grill, will be slowly pulsing all the way through this process.
At the 97 - 98% point, the car will throttle back the demand to around 3.5 - 3.6 kw's until the SOC reaches 100% and a fully charged state.
The car will report 100% complete at this point on the dash panel.
With car STILL plugged in of course, the balancing of the HV pack will now commence.
At this point, the MG badge is now displaying a constant soft glow.
My energy meter is now reporting a draw of only around 500 Watts.
I can tell when the balancing is pretty much complete, because the draw will reduce right down to 300 Watts.
Shortly after this, I can hear the wall box "Cluck" to indicate that the car has finished balancing the pack.
IF your pack has been affected by the introduction of one of the "Buggy" updates, then balancing of your cells is going to take a long time, to correct at first.
This will situation will improve as the pack returns to a normal state of balance.
The max time the car will attempt to balance the pack, is about 10 hours.
IF after this, it has NOT achieved the task, it will end the process and give up basically.
If so, it will try again on the next charge / balance cycle.
Your car can offer you a very crude way of displaying the level of imbalance, if you care to measure it.
Next time you plug in to carry out a charge, it will report on the dash panel, just how long it is likely to take, until it hit's 100% fully charged.
Make a note of the completion time and check the status of the MG badge, close to this end point in time.
When the MG badge has switched from the pulsing status, to a displaying a constant glow, you are now into the balancing stage.
Now keep checking back on the car, about roughy every hour.
When the MG light goes completely OUT - The car has finished balancing.
This can take ANYTHING from 1 to 5 hours ish.
The longer it takes, gives a rough idea of the level of imbalance in the pack.
Like a say, a bit crude, but not far off the mark !.
A lot of people get really stressed over this "Balancing Thing" - Don't !.
Unless your car has been badly affected by one of the "Buggy" updates ( and trust me you would have a good indication regarding power and range etc ) then I would balance about once a month if your usage charging / usage is small.

 

[JodyS21]

@Cliff Mitchell .
I have kept a pretty good eye on my home energy meter over a number of charge / balance processes.
How sad is that !.
And it reports in the following manner.
From the onset of charge commencing, from a fairly low SOC - the energy meter will briefly report a draw of 3.5 kw's then will quickly jump straight up to just above 7.1 kw's.
It will pull 7.1 ish kw's until the SOC reaches around the 97 - 98% mark.
The MG badge on the grill, will be slowly pulsing all the way through this process.
At the 97 - 98% point, the car will throttle back the demand to around 3.5 - 3.6 kw's until the SOC reaches 100% and a fully charged state.
The car will report 100% complete at this point on the dash panel.
With car STILL plugged in of course, the balancing of the HV pack will now commence.
At this point, the MG badge is now displaying a constant soft glow.
My energy meter is now reporting a draw of only around 500 Watts.
I can tell when the balancing is pretty much complete, because the draw will reduce right down to 300 Watts.
Shortly after this, I can hear the wall box "Cluck" to indicate that the car has finished balancing the pack.
IF your pack has been affected by the introduction of one of the "Buggy" updates, then balancing of your cells is going to take a long time, to correct at first.
This will situation will improve as the pack returns to a normal state of balance.
The max time the car will attempt to balance the pack, is about 10 hours.
IF after this, it has NOT achieved the task, it will end the process and give up basically.
If so, it will try again on the next charge / balance cycle.
Your car can offer you a very crude way of displaying the level of imbalance, if you care to measure it.
Next time you plug in to carry out a charge, it will report on the dash panel, just how long it is likely to take, until it hit's 100% fully charged.
Make a note of the completion time and check the status of the MG badge, close to this end point in time.
When the MG badge has switched from the pulsing status, to a displaying a constant glow, you are now into the balancing stage.
Now keep checking back on the car, about roughy every hour.
When the MG light goes completely OUT - The car has finished balancing.
This can take ANYTHING from 1 to 5 hours ish.
The longer it takes, gives a rough idea of the level of imbalance in the pack.
Like a say, a bit crude, but not far off the mark !.
A lot of people get really stressed over this "Balancing Thing" - Don't !.
Unless your car has been badly affected by one of the "Buggy" updates ( and trust me you would have a good indication regarding power and range etc ) then I would balance about once a month if your usage charging / usage is small.

Do you have your charging data in a spreadsheet, only at that point is it sad (I have...) lol!!!

So it’s only 200ish watts it’s pulling during balancing, that’s what I thought it was.
I can’t remember what bms you’re on?
Could the different BMS be causing different balancing power draw???
I know one of the faults with one of the previous bms versions was “long balancing times”. I can’t imagine it would change how much power it uses when balancing realistically.

I know we/the manual generally say AC charge & balance once a month, but realistically it’s down to usage, the more you charge & discharge (so effectively miles driven) the more the battery will be out of balance.
Of course it is chemistry as well, some battery packs just by luck could have more matched cells than others. I presume there’s no testing and cell matching going on when they assemble the packs.

 

[Cliff Mitchell]

Be careful, it may not have actually completed the balancing process.... The car will only balance for (we think) 10 hours maximum at a time.
If you have not ever balanced, it may take longer than the 10 hours to actually finish the balance.

I would suggest to be on the safe side, that after doing a few miles in it, you put it on AC charge again and let it go through the balance process again.
I have a little cctv camera in the front window that I can use to see when mine starts the balance and it completes, it's the only way I actually know what it is up to!
(I fully AC charge 3-4 times a week, so mine never needs to balancing for much more than a couple of hours anyway)

My estimation of charging time was about 10 - 11 hours to get to 100%. Based on that the balancing component took less than 2 hours.

 

[aleks57]

I have a BMS with version 02.21. the charging power drops after reaching 98% of the battery capacity. When balancing, the power consumption is 1.7 kW, the battery charge current is 350-400mA and lasts exactly 2 hours. V = 450v.

 

[Lovemyev]

Do you have your charging data in a spreadsheet, only at that point is it sad (I have...) lol!!!

So it’s only 200ish watts it’s pulling during balancing, that’s what I thought it was.
I can’t remember what bms you’re on?
Could the different BMS be causing different balancing power draw???
I know one of the faults with one of the previous bms versions was “long balancing times”. I can’t imagine it would change how much power it uses when balancing realistically.

I know we/the manual generally say AC charge & balance once a month, but realistically it’s down to usage, the more you charge & discharge (so effectively miles driven) the more the battery will be out of balance.
Of course it is chemistry as well, some battery packs just by luck could have more matched cells than others. I presume there’s no testing and cell matching going on when they assemble the packs.

Hi @JodyS21 .
I am running on the Jan 15th 21 BMS update, I think I must have been one of the first privately owned cars to receive it.
It was applied under MG Tech instructions, after the dealer who was carrying out the first service and drivers door wiring loom, rendered the car “Dead” !.
It was stuck on a ramp for three days.
Arh …… You remember it now !.
So, yeah - The car behaved strangely at first when I got it home, when plugging in, some times it would pull 7.5kw’s and then the next time it would only pull 3.5 kw’s ?.
The wall box was not the issue, it was the car acting strange.
This action continued for about 14 days regardless of what state of SOC the car was at prior to charging.
This made it extremely difficult to judge how long and how much the car was likely to receive on a timed overnight charge.
This is where the obsession with watching the energy meter started of course !.
It could actually tell me what the car was pulling and when.
I would watching this little black box almost on the hour, every hour !.
Making notes along the way, as I went.
Then after about 10 to 14 days, the car just started demanding the full 7.5kw’s when connecting to the wall box, every single time.
Which I am very grateful for, because try explaining this situation to a dealer to rectify !.
The observations of the cars charging behaviour and the effect on the energy meter became all consuming at the time.
So, like most people the car will demand roughly about 7.1 ish Kw’s when placed on charge.
It pulls this 7.1 ish kw’s until around the 97 - 98% SOC mark, then the car throttles back the draw by about 50% to about 3.5 kw’s.
Which does make sense to me.
I know a rapid charger is much different, but they start to throttle back the charge at about 80% SOC.
Reducing the high rate of load towards the end of the charging cycle, on a charger must be kinder of the HV battery.
Slamming a high load into a pack and then suddenly just stopping it at 100% SOC can not be good ?.
Back to my actual observations now.
Yeah ….. So at about the 98% SOC it reduces the pull down to 3.5kw’s.
Then at 100% it enters the balancing stage and the demand is throttled back even further.
Now we are only pulling around 500 Watts to start with, then this reduces ever more down to 350 watts and then to around 175 watts just before the balance completes and closes down the demand from the wall box.
Prior to the first service, I was running on the original factory software ( 456 volts ).
The car only had the Comfort 2 update but did not display any signs of receiving any of the affects of the “Buggy” software.
But my charging habits pre the problem in Jan 21 - would be that I would charge to a SOC that would suit our situation of journey demands.
I would only charge to 100% IF we had a long trip to make.
Therefore, I would regularly only charge to around 80% - trying to be kind to my battery.
It could be said that my battery was a little out of balance when the car was offered for service then ?.
The balancing process prior to the problems, would only take about 1 to 2 hours max, so I don’t think it was that far out of whack ?.
When I received the car back after the update, due to the charging problems that I mentioned earlier, the car was taking a stupid amount of time to charge and balance from my wall box.
Once the car was hooked up for over 12 hours !.
Over the last 4 - 5 months I have charged successfully ( thank the Lord ) but I still think it takes longer to complete a balance than when I was on the factory OEM software.
The last time I timed it, it was around 3 hours to balance.
Just for reference, the car is now 18 months old and we have covered 12.500 miles.
The car drives absolutely fine and due to the lift in restrictions in Wales, we have been able to make some longer trips that has stretched the range.
The GOM is reporting a pretty good actual rate of consumption.
But when making a longer journey, I do like to reset the accumulative trip before commencing the trip.
I am just more comfortable with it this way.

 

[JodyS21]

My estimation of charging time was about 10 - 11 hours to get to 100%. Based on that the balancing component took less than 2 hours.

In that case it must've completed the balance.

I am surprised that given you've done 3500km in 3 months and never done a balance before, that it only took 2 hours to balance. Sounds like you've got well matched battery cells in your pack.

Unfortunately the only way to know for sure about any battery imbalance is to get an ODB2 device and app to check out the battery cell min/max voltages.

 

[JodyS21]

I have a BMS with version 02.21. the charging power drops after reaching 98% of the battery capacity. When balancing, the power consumption is 1.7 kW, the battery charge current is 350-400mA and lasts exactly 2 hours. V = 450v.

350-400mAmps @ 450V is 180Watts, so that roughly matches the 200watts that @Lovemyev has recorded.
I don't quite get where your 1.7kW comes into it?
If your balancing is lasting 2 hours @ 400mA/180Watts, then it will have used 360kWh of power to do the balance.

The length of time it takes to balance depends on how imbalanced the battery is, we "know" it can only balance(move) a tiny amount per hour, I can't remember the figure - 1mA per hour or was it 10mA? that is the amount it can change/move per (180) cell I think it was (or is was it per cell pack (9)...
Also, I think we worked out from various peoples figures that it stops balancing once the min to max cell difference is down to about 0.016-0.020Volts. This figure could easily be a BMS configured number.

 

[Lovemyev]

350-400mAmps @ 450V is 180Watts, so that roughly matches the 200watts that @Lovemyev has recorded.
I don't quite get where your 1.7kW comes into it?
If your balancing is lasting 2 hours @ 400mA/180Watts, then it will have used 360kWh of power to do the balance.

The length of time it takes to balance depends on how imbalanced the battery is, we "know" it can only balance(move) a tiny amount per hour, I can't remember the figure - 1mA per hour or was it 10mA? that is the amount it can change/move per (180) cell I think it was (or is was it per cell pack (9)...
Also, I think we worked out from various peoples figures that it stops balancing once the min to max cell difference is down to about 0.016-0.020Volts. This figure could easily be a BMS configured number.

I am a little confused over the 1.7 figure myself .

 

[JodyS21]

Hi @JodyS21 .
I am running on the Jan 15th 21 BMS update, I think I must have been one of the first privately owned cars to receive it.
It was applied under MG Tech instructions, after the dealer who was carrying out the first service and drivers door wiring loom, rendered the car “Dead” !.
It was stuck on a ramp for three days.
Arh …… You remember it now !.
So, yeah - The car behaved strangely at first when I got it home, when plugging in, some times it would pull 7.5kw’s and then the next time it would only pull 3.5 kw’s ?.
The wall box was not the issue, it was the car acting strange.
This action continued for about 14 days regardless of what state of SOC the car was at prior to charging.
This made it extremely difficult to judge how long and how much the car was likely to receive on a timed overnight charge.
This is where the obsession with watching the energy meter started of course !.
It could actually tell me what the car was pulling and when.
I would watching this little black box almost on the hour, every hour !.
Making notes along the way, as I went.
Then after about 10 to 14 days, the car just started demanding the full 7.5kw’s when connecting to the wall box, every single time.
Which I am very grateful for, because try explaining this situation to a dealer to rectify !.
The observations of the cars charging behaviour and the effect on the energy meter became all consuming at the time.
So, like most people the car will demand roughly about 7.1 ish Kw’s when placed on charge.
It pulls this 7.1 ish kw’s until around the 97 - 98% SOC mark, then the car throttles back the draw by about 50% to about 3.5 kw’s.
Which does make sense to me.
I know a rapid charger is much different, but they start to throttle back the charge at about 80% SOC.
Reducing the high rate of load towards the end of the charging cycle, on a charger must be kinder of the HV battery.
Slamming a high load into a pack and then suddenly just stopping it at 100% SOC can not be good ?.
Back to my actual observations now.
Yeah ….. So at about the 98% SOC it reduces the pull down to 3.5kw’s.
Then at 100% it enters the balancing stage and the demand is throttled back even further.
Now we are only pulling around 500 Watts to start with, then this reduces ever more down to 350 watts and then to around 175 watts just before the balance completes and closes down the demand from the wall box.
Prior to the first service, I was running on the original factory software ( 456 volts ).
The car only had the Comfort 2 update but did not display any signs of receiving any of the affects of the “Buggy” software.
But my charging habits pre the problem in Jan 21 - would be that I would charge to a SOC that would suit our situation of journey demands.
I would only charge to 100% IF we had a long trip to make.
Therefore, I would regularly only charge to around 80% - trying to be kind to my battery.
It could be said that my battery was a little out of balance when the car was offered for service then ?.
The balancing process prior to the problems, would only take about 1 to 2 hours max, so I don’t think it was that far out of whack ?.
When I received the car back after the update, due to the charging problems that I mentioned earlier, the car was taking a stupid amount of time to charge and balance from my wall box.
Once the car was hooked up for over 12 hours !.
Over the last 4 - 5 months I have charged successfully ( thank the Lord ) but I still think it takes longer to complete a balance than when I was on the factory OEM software.
The last time I timed it, it was around 3 hours to balance.
Just for reference, the car is now 18 months old and we have covered 12.500 miles.
The car drives absolutely fine and due to the lift in restrictions in Wales, we have been able to make some longer trips that has stretched the range.
The GOM is reporting a pretty good actual rate of consumption.
But when making a longer journey, I do like to reset the accumulative trip before commencing the trip.
I am just more comfortable with it this way.

I remember now!
So nothing was actually done by the dealer to "fix" it from being restricted to 3.5kW instead of the full 7.xkW / or by something changing on the "AC fast charger wall box"?

I imagine if you think about it that there's a max charge power against SOC% graph that the BMS effectively follows whether it's AC or DC.
0-80% it probably allows the maximum (80kW) power. Then it tapers off until at 98% whether it's being given direct DC or AC power it reduces down to a slow trickle to protect the batteries. All temperature dependant too obvs.

They definitely said that one of the issues with a previous BMS was it taking a long time to balance, so there was clearly something going on with BMS versions in regard to it.
Given (we think) it's just "burning" off the power it doesn't want when balancing using resisters, there must be a hard limit to the amount of power it can safely use when balancing. So the BMS can lower the balance power it if it wants but won't ever be able to make it too high - I presume this must've been what the issue with the previous BMS must've been?

Thinking about it, no ones ever said anything about the 10 hour balance limit being different between BMS versions, it's possible it changed - maybe it was limited to only doing it for a couple of hours on early BMSs and that caused peoples balance to get further out of whack?

 

[Cliff Mitchell]

In that case it must've completed the balance.

I am surprised that given you've done 3500km in 3 months and never done a balance before, that it only took 2 hours to balance. Sounds like you've got well matched battery cells in your pack.

Unfortunately the only way to know for sure about any battery imbalance is to get an ODB2 device and app to check out the battery cell min/max voltages.

To be honest I am fascinated by the technical knowledge and commitment to detail demonstrated by the contributors to this forum. I bought the car because I like to drive it, and it suits my daily driving needs. After reading this forum for a while and taking what I think seems like reasonable advice, I take a very simple approach.

I believe that using my charger on 15amps only, charging overnight from anywhere from 30% charge up to 80 - 90% seems to give me a consistent return.

Almost exactly every time I receive 19.8 kilometers per hour charging, 5.8 kilometers per kwh of charge, power delivery is at 3.3 kws, at a cost of 2.6 cents per kilometer.

 

[Lovemyev]

I remember now!
So nothing was actually done by the dealer to "fix" it from being restricted to 3.5kW instead of the full 7.xkW / or by something changing on the "AC fast charger wall box"?

I imagine if you think about it that there's a max charge power against SOC% graph that the BMS effectively follows whether it's AC or DC.
0-80% it probably allows the maximum (80kW) power. Then it tapers off until at 98% whether it's being given direct DC or AC power it reduces down to a slow trickle to protect the batteries. All temperature dependant too obvs.

They definitely said that one of the issues with a previous BMS was it taking a long time to balance, so there was clearly something going on with BMS versions in regard to it.
Given (we think) it's just "burning" off the power it doesn't want when balancing using resisters, there must be a hard limit to the amount of power it can safely use when balancing. So the BMS can lower the balance power it if it wants but won't ever be able to make it too high - I presume this must've been what the issue with the previous BMS must've been?

Thinking about it, no ones ever said anything about the 10 hour balance limit being different between BMS versions, it's possible it changed - maybe it was limited to only doing it for a couple of hours on early BMSs and that caused peoples balance to get further out of whack?

No - I tried to resist submitting back to the dealer after the last episode !.
Nothing was touched in the car or the wall box !.
It ( for some unexplained reason ) started to charge correctly by pulling 7.1 kw’s ( as it should ) from a low state of charge ?.
Only tonight, I have decided to let the car fully charge and then balance.
We have a longer trip to make in the morning ( Monday ) and I want to do the outward and home trip on the single charge.
So, I have allowed the car to fully charge then balance.
It did the very same cycle, charged at 7.1 kw’s right up to around 97 - 98% - Then the car reduced the charge from the wall box, down to about 3.5 kw’s until it hit 100% fully charged.
At this point, my energy meter dropped to displaying about 500 ish Watts.
The car then reduced the demand right down again, when the balance was near to completing ( about 175 kw’s ).
Shortly after this, it stopped receiving anything from the wall box by opening the conductor inside the box with a “Thump”.
As best as I could tell from my energy meter, the balance time had taken just over three hours ( ish ).
Still a little longer than I expected and a bit more time than it did ( I think ) on the previous OEM factory software.
From memory, the balance then would usually take roughly, about one hour ( ish ).
I must truly admit, that I don’t balance every time I charge.
I only charge to a SOC that will cover our requirements over the coming days.
Shorter trips, I tend to only charger to around 80 - 85 %.
If I am travelling further, then I will charge to 100% and then allow the pack to conduct a balance cycle at the end.
The latter BMS update ( 15th Jan 2021 ) does give a bigger buffer at the top of the pack I believe.
This is very evident, because stronger Regen is even available when the car is fully charged !.
To have this higher level of Regen at the higher given SOC - then this regained energy has to go somewhere !.
It is being given back into the space created in the pack, by the latest update in my opinion.
It is welcome of course, but the car does react differently than it did prior to the update, but in a good way !.
I have to admit, that I have stopped stressing / chasing / matching the same balancing pack time, as the older BMS update.
Repeatability charging to the Max and then more & more hours of charging in an attempt to restore the shorter balance time has kind of taken a bit of a back seat now.
Of course, I do still carry out a balnce process, but not every single time I charge.
It becomes obsessive if you are not very careful !.
Banging the HV battery right up to 100% fully charged - then have it sit there for a couple of days, does not sit well with me sorry.
Pre update, I would charge to suit our travel needs, short trips locally and I would charge to about 80 - 85% SOC.
If I had a longer trip to take, then yes of course I would charge to 100% and then allow the charger to balance the pack.
What is right and wrong, will only manifest itself in years to come I guess ?.
I just don’t hold with the idea of fully charging the HV pack and then not using the car for days on end, leaving the pack bursting to capacity, can not help with the long term health of the HV battery surely ?.
I know will say that this is not important, because if the buffer at the top of the pack !.
But if MG have increased the size of this upper buffer on the latest update ( and the cars leaving the factory are in the same condition ) then why have they done this ?.
I personally think they are looking to protect the life cycle of the HV packs somehow.

 

[Coulomb]

I imagine if you think about it that there's a max charge power against SOC% graph that the BMS effectively follows whether it's AC or DC.

The limit should, and probably is, based on the highest stress on any cell. That stress is usually high cell voltage, but it could be temperature (too high or too low). It might sometimes be limited by charger temperature.

Under similar conditions, you expect to find much the same charge power versus SOC graph for either AC or DC charging, though of course AC charging will be clipped at the rated power of the on board charger (6.6 kW output I believe, which often seems to come to 7.1kW at the AC input). There isn't a charge curve stored in a ECU somewhere: it "emerges" as a property of the cells.