Balance Charging - a few questions

[2Sheds]

A few EV noob questions

I have had my phase 2 Trophy for about 2.5 months now, and as it is owned not leased, I am keen to keep the battery in as good a state of health as I can. With that in mind I have been cycling it between around 20-80% as per recommended practice. The thing is that we aren't doing a lot of mileage, particularly after the first couple of weeks of getting the car, and I've been waiting for a long while now for a charge cycle to fall just before a long run to do a balance charge, so the car doesn't sit around at 100%. Just isn't happening though! As a consequence I haven't yet done a balance charge ?. (It was at 100% when we picked it up though). So far the car has done about 1400 miles, been exclusively charged at home, averaging about once every ten days or so (using Ohme charger, not granny lead) with the exception of one 25% top up at a 50kW rapid. So...I have a few questions:

1) The recommendation is to perform a balance charge once a month. So is this requirement purely a time based thing, or is that just based on an average usage? In other words, is it ok to do it less often if the car is used infrequently/does light mileage?

2). Does it matter what SoC the battery starts off at when doing a balance charge, ie is it ok to do it from 80%, 60%, whatever, or should it be a from low SoC? (I think I read somewhere that the battery should be occasionally charged 10-100%). I ask this so that if we do a longer trip in-between the normal 20-80% routine, I could balance it then, eg if it was at 60%.

3). Am I overthinking this? I am worrying too much about it?!

Thanks in advance.

 

[AndyL61]

State of charge.

 

[Corindikev]

I have never seen the term "Trickle Charging" on the infotainment screen but it is likely that it says that as soon as the full rate 6.6kW (or thereabouts) slows after the battery SOC reaches the set point until it slows down beyond a certain rate and then says "Balancing".

For general round town running etc you should set the charge point to 80% for the 64kWh & 77kWh batteries as these use the NMC chemistry. This is recommended for the best battery SOH (State of Health). About once a month a full 100% charge & balance is a good idea even if you do not go on a long trip.

The battery will not balance when charged by a fast or super fast DC charger which is what most public chargers are and range from 50kW to 350kW. If you use DC chargers for a long time without AC slow charging the balance will get to the point where you will get a message on the infotainment screen requesting an AC slow charge and balance.

I have tested the balancing process and if set even at 60% a balance will take place at the end of charging so setting at 60%, 70%, 80%, 90% or 100% a battery balance will always take place. You should always leave the charging cable in place until the car says charging complete.

 

[Rolfe]

It happens automatically when you leave the car plugged in to AC charging and it gets to 100%.

Yes, it likely does, after standing in car yards, on a ship, etc.

That's the first stage of balancing.

That's the indication that it's balancing. I wish MG made it more obvious. Many users would look at that and say "oh, it's full, I can pull out the plug now".

I believe so, yes.

Yes, unless you really need to drive the car.

Once it's balanced, yes, charge whenever you feel like (no need o wait till it gets down to 20%), but only to 80% except once a month, or when you know you'll need the extra range.

The amount of time it spends balancing depends on many factors, basically how unbalanced the battery is. The very first balance is expected to take longer; it may even take several hours, or it might give up and try again next time you charge to 100%.

That bit about new owners just pulling the plug because it says 100%, that was me. I was watching the app (new owner, right?) and saw the "finish time" continually updating to the current time and had no idea what was going on so I just stopped it. At that time the app showed two figures after the decimal point and if I'd looked I'd have seen that the car was drawing 20 watts (0.02 kW) but I didn't see that. Now it's even worse because it just reads 0.0 kW.

It took the good people on the forum here to explain it to me, and the next time I watched, and the readout changed to "not charging" and no finishing time or charging power showing after about half an hour. The message is, just leave it and don't unplug or stop the charge unless you need the car in a hurry, it knows what to do and it will simply do it.

I think it won't resume the balance if it's interrupted. One day I was charging from solar using eco+ on the Zappi and the sun went behind a cloud just as balancing was about to start. Charging stopped and didn't restart. I thought maybe I should do something and plugged in the granny charger but nothing happened. Next time that happened I made a trip to the bottle recycling centre about a mile away with the empties then plugged in the granny charger when I got back. That worked.

Disclaimer, LFP battery here. The NMC doesn't behave quite the same way. The LFP likes to balance at 100% every time it's charged and the time is pretty constant at 30 to 35 minutes. I believe the NMC is a lot more variable. Just leave it alone, go and do something else, and let it get on with it.

 

[wattmatters]

Disclaimer, LFP battery here. The NMC doesn't behave quite the same way. The LFP likes to balance at 100% every time it's charged and the time is pretty constant at 30 to 35 minutes. I believe the NMC is a lot more variable. Just leave it alone, go and do something else, and let it get on with it.

Yep, the car's battery management system will look after it, and if it needs intervention it will let you know.

LFP needs to be at/near 100% to balance. Below that and the cell voltage differences are not so apparent, indeed attempting to balance at lower SOC can have the opposite effect.

With NMC cell voltage differences are far more apparent at pretty much at any SOC and so it can be balanced at different SOC levels (e.g. if you set the charge limit to 80% it will do some balancing at the end). But ultimately just correcting for cell voltages differences isn't enough, it still needs a deep discharge and full 100% charge occasionally to account for any capacity variances between cells. How occasionally depends on how the car is used and charged. If you do lots of DC fast charging then doing a longer AC charge (≤11 kW) at least monthly is a good idea.

 

[Coulomb]

I think it won't resume the balance if it's interrupted.

On my Mark 1 ZS EV, I find that if I leave it for 10 minutes since the charging stopped, it would balance again if needed. Things could be very different with other models, especially if it has an LFP battery.

I find that mine won't always start balancing at the end of a charge. Hence my efforts to try and restart it. My most recent charge was like that, although I might not have noticed a period of low charge power. When I plugged it in 10 minutes later, it balanced for 55 minutes.

 

[Rolfe]

Might be my LFP battery.

 

[Evgen K]

MG4 Trophy/Luxury, does it do battery balancing if my charge level is limited by 80% (health mode)

 

[siteguru]

Yes it does.

But balancing at 100% once per month is still recommended.

 

[Ian Key]

MG4 Trophy/Luxury, does it do battery balancing if my charge level is limited by 80% (health mode)

Yes but it will balance the individual cells to 80% each so the last 20% won't be balanced so any underperforming cells will not be brought up to the optimal level of performance.

 

[Evgen K]

Yes but it will balance the individual cells to 80% each so the last 20% won't be balanced so any underperforming cells will not be brought up to the optimal level of performance.

Thank but seems i don't understand you completely, I thought it didn't matter at what level the car did the balancing..

 

[siteguru]

Balancing at other levels doesn't really hurt*, but the best outcome is achieved by balancing at 100% as that makes sure all cells are at their optimum level.

* Other than balancing at, say, 80% may equalise all cells at the level of the worst-performing cell.

 

[barry7153]

The recommended usage/working range of the battery seems to be 20 - 80% for optimum lifespan. What would be the detrimental effect, if any, of always home charging 15 - 90%. I like 90% as that is the upper charge limit of OPD.

 

[Rolfe]

Probably not much, especially if you didn't leave the car at either extreme for days on end.

 

[HazardLights]

I am thinking about charging my Trophy to 100% before trips where the round trip requires a charge (if I charge to my usual 70% or even 75% before the trip) and getting my balancing then. I am currently doing more than one such trip a month but don't expect that to be the norm. I am on the one hand inclined (as a new owner or obsessive) to stick to charging to no more than 75%, however on the other I think that I should chill and charge more if it reduces range anxiety.

I suspect my 100% charge frequency will be higher than I need for balancing. My weekday mileage is only twenty and a bit miles a day in a 45-70% range.

PS- for daily use, if you can I'd aim for a 70 or 75% charge limit and keep going over 75% trips where you will need to recharge before you get home.

 

[tsedge]

There are two different activites that are important:

- Balancing: equalising cell voltages, can be done at a range of SoC but typically at 80% or higher. All this does it try to equalise the cell voltages, so that they don't diverge and reduce the range (governed by the lowest voltage cell).

- Calibrating: measuring the maximum (or minimum cell ranges). Requires charge to 100% to properly calibrate max, discharge to 10% for min (or at least near min).

Both matter, (the pack changes as it ages), which is why the recommendations are to charge to 100% regularly and periodically discharge to 10% followed by 100% charge.

Balancing at 100% also achieves Calibration, so it is convenient to cover both with one stone.

Almost certainly people are worrying about this far too much. Just use your car and don't leave it for weeks at a very high SoC, that's really the only thing to avoid.