Charging Routine

Cocijo said:

Very informative - thank you. Do you know why they should be charged to 100%? I guess in a none technical sense i’ve aleays thought a fully charged pack puts stress on the cells and should not be left for a long time in this state - how is this not the case with LFP do you know? So I guess it’s ok to leave your car fully charged for a long time with LFP?

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It is down to the chemistry of the electrolyte between the Anode and Cathode. With the Li-Ion cells, we have become familiar with the electrolyte attacks on either the anode or the cathode depending upon whether they have a very low or very high SOC. Hence regularly charging to 80% only is recommended. In reality of course there is a buffer above that 100% SOC which is notified to the user and this is to prevent the chemistry from becoming very destructive Li-Ion is most stable at around 50% SOC. However, LEP chemistry is very different and is stable at 100% charge and cell manufacturers, therefore, recommend regular complete charging to 100%. One example of this with LEP Home Storage used with Solar PV I was recently looking at for my home was that the user manual said that to ensure the long life of the batteries, users should program a full charge to 100% at least once a week.

Yes - that makes sense. Do you know if LFP packs have a top and bottom buffer? Is the usable capacity improved from li-ion?

If there are optimum ways to keep the batteries in tip top condition depending on the battery, are the manufactures guiding the owners with this information ?

Cocijo said:

Yes - that makes sense. Do you know if LFP packs have a top and bottom buffer? Is the usable capacity improved from li-ion?

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I don't know any details on what the buffers are on the MG ZS SR but they would have to have a bottom buffer for sure. Speaking to Miles Roberts of the Chorley Group earlier this week after the Podcast he said that even though the ZS LR has LFP the Charging menus on the SR are the same as LR so there is still an 80% indicator on the screen although he didn't think it did very much since the car should be charged to 100%. there needs to be much more education about this. Tesla is the other mainstream EV company with lots of LFP cars coming into customers' hands and I believe they make it clear initially or the recommended daily charging level. I think people who have driven EVs for some time will find it instinctively wrong to charge to 100% all the time but we all need a little more transparency about what the battery needs to get the best out of it. Cross fueling Diesel in a Petrol car or vice versa is the ICE equivalent although it has a more immediate effect. If you put a little Petrol in a Diesel car's tank providing it's not empty of diesel you can probably get away with it at first, but it will have accelerated engine wear and damaged the fuel pump although the car will run. Charging in an inappropriate way at first you'll probably not notice but at some point, the range will suffer because the battery will not accept as much charge.

Keep an eye on upcoming podcasts on the forum because this and Home PV and Battery Storage will be on the agendasoon.

I typically charge my car to 100%. After a year and 9000 miles at the annual service the car was reported as showing zero degradation so I don't think charging to 100% is having a significant impact on the battery.

Rocinante said:

If there are optimum ways to keep the batteries in tip top condition depending on the battery, are the manufactures guiding the owners with this information ?

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It is patchy but were are hoping to address this on an upcoming Podcast possibly along with home storage batteries.

Prof1967 said:

I typically charge my car to 100%. After a year and 9000 miles at the annual service the car was reported as showing zero degradation so I don't think charging to 100% is having a significant impact on the battery.

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Great, I'm glad you're happy with the way your charging routine is working for you. However, remember that there is a top buffer on your battery pack so that when you see 100% that is 100% not of what your battery pack could physically charge to but 100% of the usable battery. This buffer is there because every cell in the pack is slightly different and therefore if your car's BMS just let you keep charging until it could physically take no more the cells the first cells to reach their maximum would fry as you kept pumping power in which they couldn't accept. Also, it is a physical fact that cells degrade through a number of factors including age/time, charge cycles, State of Charge and temperature. Therefore, your battery cells will have degraded in a year, 9000 miles and charging to 100% it is just that the degradation may have been minimal if, for example, you didn't leave your car with 100% charge without driving it soon after.

The "Typical Cell Voltage Curve" for a LiIon battery cell (below) illustrated why charging up to 80% and discharging down to 20% is the range that the battery prefers to operate in. When the battery is charged above 80% the elevated cell voltage maked the chemicles in the cell more reactive and accelerates degrgation. It is also worth saying that in that area of the curve which rises steeply when on a Rapid Charger for instance the charge rate dropps (ie above 80% SOC) charging losses are greater as cell resitance to chargeing rises and more power is lost through heat loss.

BarryH said:

It is patchy but were are hoping to address this on an upcoming Podcast possibly along with home storage batteries.

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Surely it's in all the manufacturers interests to advise people the best way to charge their cars to maintain the batteries, if it makes a recognisable difference, much as they would tell you what oil to put in your engine, and what servicing it needs, (or what fuel to put in). If it is understood, surely they should pass this on clearly and unambiguously, and people shouldn't have to seek out this information or interpret voltage charts.

Or perhaps the fear is that guidance could be seen as 'restrictions' on charging and another layer of complexity, and reduce EV take up ?

Rocinante said:

Surely it's in all the manufacturers interests to advise people the best way to charge their cars to maintain the batteries, if it makes a recognisable difference, much as they would tell you what oil to put in your engine, and what servicing it needs, (or what fuel to put in). If it is understood, surely they should pass this on clearly and unambiguously, and people shouldn't have to seek out this information or interpret voltage charts.

Or perhaps the fear is that guidance could be seen as 'restrictions' on charging and another layer of complexity, and reduce EV take up ?

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Certainly it's your last point. Any admission that the batteries require some kind of thoughtful protection would add to the narrative that batteries will die and need replacing. They're confident that whatever you do will be within the tolerance of the warranty so they simply don't need to worry people.

The objective truth is that you can't avoid battery degradation - it is inevitable - but you can mitigate it. However, it's generally too complicated to explain the nuances to your average end user so they keep the advice simple and not too scary. Some manufacturers build in a big buffer which (contrary to popular opinion) doesn't prevent all degradation but certainly reduces it significantly and (probably more significantly) provides a place to hide the initial degradation. That's how they're able to confidently tell you that your battery still has 100% state of health, even though it's a widely known fact that batteries degrade more in the first year than at any other time.

The manufacturers keep things in layman's terms so as not to put people off.
Basically, buy an EV, charge it up and drive it, then when the car says, "low battery" charge it up again and drive it again.
This and a once a month equalisation charge is all you actually need to do to fulfill the warranty terms where they guarantee the battery capacity will still be 70% or more after 7 years.

Petriix said:

Certainly it's your last point. Any admission that the batteries require some kind of thoughtful protection would add to the narrative that batteries will die and need replacing. They're confident that whatever you do will be within the tolerance of the warranty so they simply don't need to worry people.

The objective truth is that you can't avoid battery degradation - it is inevitable - but you can mitigate it. However, it's generally too complicated to explain the nuances to your average end user so they keep the advice simple and not too scary. Some manufacturers build in a big buffer which (contrary to popular opinion) doesn't prevent all degradation but certainly reduces it significantly and (probably more significantly) provides a place to hide the initial degradation. That's how they're able to confidently tell you that your battery still has 100% state of health, even though it's a widely known fact that batteries degrade more in the first year than at any other time.

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Spot on. The top buffer hids the initial degradation and this was something that Nissan failed to do with the early LEAF. They were keen to have a high (for the time and available tech) capacity and so there was very little top buffer and their "Guaranty" was that the battery would have 70-% of the capacity new after the 8 years (if I recall) use. they offered a battery replacement in the event of it failing. Later models, Nissan seemed to have learned the lesson a little although last time I checked they were still inclined to publish a higher battery than the actual User Available capacity to the user whereas other makers tend to publish the useable capacity. I use "EV Watchdog" App with an OBD2 Dongle on my ZS and it shows on the SOC screen both the SOC % of the actual capacity and SOC % usable capacity. Therefore I can see a 100% useable SOC, but also the lower SOC % of the actual Battery.

BarryH said:

Therefore I can see a 100% useable SOC, but also the lower SOC % of the actual Battery.

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So how much degradation has there been with the "actual battery" ?

Rocinante said:

So how much degradation has there been with the "actual battery" ?

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There is actually a State of Health (SOH) on one of the screens which tells me:-

"Battery SOH 93.7% [-0.2 since last time]"

This means in 16,600 miles in coming up for 28 months the pack has a 6.3% degradation overall. This may be influenced by the lowest voltage cell in the 108 cell pack

The screen also shows that the Capacity of the Pack at 93.7% is 100.6 Ah and the Charge 9ie SOC) is 43.5% and 49.2 Ah

Alb said:

Had the car for a month now and I don't think the state of charge has ever dropped below 80%.
I'm not doing any long journeys so do you think it would be better for the battery if I ran it down and maintained it a much lower state of charge?
I'm only using the Granny at the moment so charging rate has only ever been low.

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Hi Alb, I've had my car for about 8months and 8600 kms and always use the granny cable to charge. I usually charge 2 times per week going up to 100% and down to roughly 30%.
Works for me.

Cocijo said:

Very informative - thank you. Do you know why they should be charged to 100%? I guess in a none technical sense i’ve aleays thought a fully charged pack puts stress on the cells and should not be left for a long time in this state - how is this not the case with LFP do you know? So I guess it’s ok to leave your car fully charged for a long time with LFP?

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Oh this is hurting my head, I can't granny or home charge so use public rapid and fast chargers. Had the car since March and never balanced charged in 3000 miles covered. Hmm, wonders if this is doing the batteries in.

Geo68 said:

Oh this is hurting my head, I can't granny or home charge so use public rapid and fast chargers. Had the car since March and never balanced charged in 3000 miles covered. Hmm, wonders if this is doing the batteries in.

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Fast charging is AC? So you’ve likely got a type 2 cable? Easiest way is to DC rapid to 90% or so and then pop on a public AC type 2. The last 10% / 5.7kWh will take a little under an hour. Then leave it on for another couple of hours whilst shopping, cinema, walking home, etc? Should be enough to balance. Maybe?

Alternatively, balancing takes very little power so could be done via granny charger at an accommodating friend/relative/unsuspecting neighbour with an unsecured outside socket!!

biffo said:

Fast charging is AC? So you’ve likely got a type 2 cable? Easiest way is to DC rapid to 90% or so and then pop on a public AC type 2. The last 10% / 5.7kWh will take a little under an hour. Then leave it on for another couple of hours whilst shopping, cinema, walking home, etc? Should be enough to balance. Maybe?

Alternatively, balancing takes very little power so could be done via granny charger at an accommodating friend/relative/unsuspecting neighbour with an unsecured outside socket!!

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Cheers, will stick it on an AC charge down at my localish charging station and leave it on all day, that should do it or as you say dc charge it if the dc is available then balance.

You cannot balance on DC and I wouldn't go over 90% on a rapid.

Jomarkh said:

You cannot balance on DC and I wouldn't go over 90% on a rapid.

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Think you got me wrong, dc up to 80ish percent then on to ac to balance.

Cocijo said:

Very informative - thank you. Do you know why they should be charged to 100%? I guess in a none technical sense i’ve aleays thought a fully charged pack puts stress on the cells and should not be left for a long time in this state - how is this not the case with LFP do you know? So I guess it’s ok to leave your car fully charged for a long time with LFP?

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Each type of chemistry has its prefered stable state. With LFP cells typically use Graphite Anode material and Lithium (Li) Iron (Fe) Phosphate (PO) material Cathode are chemically stable at 100% charge when as I understand it the Lithium "ions" produce stable bonds and therefore they are safer and less stressed than many other Lithium-based battery chemistries.

Incidentally, LFP is also more temperature stable than other Lithium-based chemistries (ie. Lithium Cobalt Oxide (LCO), Lithium Manganese Oxide (LMO), Lithium Nickel Cobalt Aluminum Oxide (NCA), Lithium Nickel Manganese Cobalt Oxide (NMC), and Lithium Titanate (LTO)) and can withstand temperatures up to 250C so a great safety margin in a car.