Minimising battery degradation

[M3P_W8]

I have a 2021 Shanghai-built M3P with the 82 kWh Panasonic battery.

My understanding is that the following four charging regimes all take the same amount of power:

1. Daily charge - 60% to 80%
2. Daily charge - 40% to 60%
3. Every other day charge - 40% to 80%
4. Every other day charge - 20% to 60%

Which is the best and worst for minimising battery degradation assuming all charging is done using a home 7kW charger?

Would the differences even be noticeable over the 3 to 4 years that I plan to keep the car?

 

[FlatSix911]

Take a look at the articles published by Battery University... BU-808: How to Prolong Lithium-based Batteries

TLDR: Figure 6 illustrates dynamic stress tests (DST) reflecting capacity loss when cycling Li-ion at various charge and discharge bandwidths. The largest capacity loss occurs when discharging a fully charged Li-ion to 25 percent SoC (black); the loss would be higher if fully discharged. Cycling between 85 and 25 percent (green) provides a longer service life than charging to 100 percent and discharging to 50 percent (dark blue).

The smallest capacity loss is attained by charging Li-ion to 75 percent and discharging to 65 percent. This, however, does not fully utilize the battery. High voltages and exposure to elevated temperature is said to degrade the battery quicker than cycling under normal condition.

 

[Durzel]

Not sure what you mean about charging regimes, are you suggesting that you’d alternate between those 4 options?

I think you’ll probably drive yourself mad trying to predict how the BMS calculates rated and actual ranges etc.

The only thing that is certain is that frequent (as in habitual) supercharging/rapid DC charging) will wear the battery, but even that I’m not sure you’d necessarily notice in a reasonable timeframe unless you’re doing mega miles.

I’m uncertain whether you’ve got the battery that can (wants to be?) charged to 100%, or whether it’s the one where leaving it at that SoC should be avoided.

As I understand it generally with these batteries having them at a reasonable mid point of charge is ideal, not too low and not too high. Beyond that you’ll be in the realms of obsessing over minor apparent reductions in range, etc.

 

[M3P_W8]

Take a look at the articles published by Battery University... BU-808: How to Prolong Lithium-based Batteries

TLDR: Figure 6 illustrates dynamic stress tests (DST) reflecting capacity loss when cycling Li-ion at various charge and discharge bandwidths. The largest capacity loss occurs when discharging a fully charged Li-ion to 25 percent SoC (black); the loss would be higher if fully discharged. Cycling between 85 and 25 percent (green) provides a longer service life than charging to 100 percent and discharging to 50 percent (dark blue). The smallest capacity loss is attained by charging Li-ion to 75 percent and discharging to 65 percent. This, however, does not fully utilize the battery. High voltages and exposure to elevated temperature is said to degrade the battery quicker than cycling under normal condition.

View attachment 705967

Thanks for that!

So if I'm understanding that chart correctly, The 'best' option for minimising battery degradation out of the 4 scenarios I proposed is likely to be #1 (daily charge from 60% to 80%). Not sure I can extrapolate to the worst case though!

 

[M3P_W8]

Not sure what you mean about charging regimes, are you suggesting that you’d alternate between those 4 options?

I think you’ll probably drive yourself mad trying to predict how the BMS calculates rated and actual ranges etc.

The only thing that is certain is that frequent (as in habitual) supercharging/rapid DC charging) will wear the battery, but even that I’m not sure you’d necessarily notice in a reasonable timeframe unless you’re doing mega miles.

I’m uncertain whether you’ve got the battery that can (wants to be?) charged to 100%, or whether it’s the one where leaving it at that SoC should be avoided.

As I understand it generally with these batteries having them at a reasonable mid point of charge is ideal, not too low and not too high. Beyond that you’ll be in the realms of obsessing over minor apparent reductions in range, etc.

'Charging regimes' was probably not the best choice of words! I am interested in the theory behind battery degradation, and was using a 20% daily battery use as a hypothetical example. e.g is it better to charge daily from 60 to 80%, every two days from 40% to 80%, or every 3 days from 20% to 80% etc. etc. (recognising there are many other 'charging regimes' if using 20% per day!)

By the looks of the chart above, its more complex than I'd hoped it would be.

I'm not hugely concerned by battery degradation, but I suspect when it comes time to part ways with my M3P in 3 to 4 years time, knowledge of this will probably be greater than it is today. I'd therefore like to minimise it where I can (without getting too obsessed by it!) so when it is time to sell the projected mileage on a full charge is better than the average for the cars mileage, whatever that might be.

For info, I have the battery that should only be charged to 100% when required for longer journeys. This is very infrequent for me, as is the use of SuC's.

 

[GeorgeSymonds]

You are right to not obsesses. For what its worth, over 5 years of ownership I've kept the car between about 35% and 80% only going outside that when I've needed it. I don't charge every day, only if I know I will need more than it has in it fairly soon as 35% is still 100 miles or so. I've not had any battery issues in that time and probably 70k miles albeit across 3 cars.

I see it like an eleastic band. Pull it too tight for too long and it starts to break down, leave it in a draw with no tension and it goes gammy and sticks together. A gentle tension works a treat. That said, the LFP batteries in the MIC SR+ are different and like being charged to 100%, but as you have a M3P that doesn't apply.

 

[GlynG]

Whatever you do to try and minimise battery degradation it wont impact on the resale in a few years time because whoever buys the car from you will not be able to obtain conclusive proof your efforts have resulted in a longer predicted battery life - so its unlikely the value of your car will be any different to anybody else's car.

I wouldn't give the battery a second thought - you have 8 years Tesla guarantee on it for a start, The battery is monitored and maintained by the BMS and thermally Tesla are well ahead of the field in looking after the batteries. I would also ignore the predicted range of the car as its just a prediction based on an algorithm from the BMS and its impossible to predict because there are so many variables.

I think too many people are obsessed with range, the overall life of the battery and become almost neurotic over what is --- just a car, - charge it, drive it, enjoy it. None of us know how long the useable life is but I'm confident 20 years will be easily achieved - and in 20 years there will be chargers available as freely as there are petrol stations now so it will matter not if your range has dropped to 200 miles - and i suspect battery reconditioners and battery swap specialists will be abundant within just a few more years anyway - and swapped at a reasonable cost.

 

[Adopado]

I see it like an eleastic band. Pull it too tight for too long and it starts to break down, leave it in a draw with no tension and it goes gammy and sticks together. A gentle tension works a treat.

That analogy works surprisingly well ... wish I'd thought of that!

 

[Dunstan]

Other than "don't leave it at 100% all day, every day", the BMS will take care of the rest. Frequent hard acceleration is the biggest electrical stress on the battery, but you'll notice it on your tyres first.

The main influence on my charging schedule is that I can put in 35% in the four hours of cheap juice from Octopus Go.

 

[candida]

in 20 years there will be chargers available as freely as there are petrol stations now so it will matter not if your range has dropped to 200 miles

Dropped to 200 miles?

That would be an increase in my M3P.

Never reached 200 miles in 12 months.

 

[Jason71]

Dropped to 200 miles?

That would be an increase in my M3P.

Never reached 200 miles in 12 months.

sounds like you have it set in "like you stole it" mode.
Might want to deactivate that for long journeys

 

[M3P_W8]

Thanks for all the comments.

To be honest, I had thought that battery degradation was 'quick and easy' to assess by calculating the range at 100% charge using the current battery percentage and estimated range. Or does Tesla adjust the estimated range based on current ambient conditions to make that more difficult?

For example, if I turn the car on when its 20°C outside with it charged to 80% and it's showing an estimated range of 250miles, that shows a 'theoretical' max range of 312.5 miles at 100%. If it was instead 0°C outside, would the car show me a lower estimated range?

 

[Adopado]

To be honest, I had thought that battery degradation was 'quick and easy' to assess by calculating the range at 100% charge using the current battery percentage and estimated range. Or does Tesla adjust the estimated range based on current ambient conditions to make that more difficult?

If you see some of the graphs that people get out of Teslafi you see it's just not a straighforward process ... in fact sometimes the battery even improves! I've had my car for just over 2 years and I don't have a clue what the degradation is ... there's nothing noticeable to me but I routinely have the display showing percentage rather than miles and I pay attention to my Wh/mile usage to keep efficiency in mind. I know that if I had a sure fire way of showing the detailed degradation of the battery it would just give me something more to worry about! If you follow general good practices in use of the car (i.e. don't go from 100% to 0% between charges and don't let it sit at a low SOC or a high SOC) there's not much you can do about it anyway.

 

[HenryT]

For example, if I turn the car on when its 20°C outside with it charged to 80% and it's showing an estimated range of 250miles, that shows a 'theoretical' max range of 312.5 miles at 100%. If it was instead 0°C outside, would the car show me a lower estimated range?

No, it wouldn't.* The 'guessometer' as some call it is based on a fixed formula so won't vary with weather or other conditions.

*(There is one exception to this, in very cold conditions you car may sometimes 'hold' a part of your battery in reserve until it warms and therefore range would only reflect the available battery capacity)

The energy graph available in your car is much more meaningful and will reflect actuality based upon driving history (etc) for up to the last 30 miles. See here

 

[kelvin 660]

Actually, the miles available @ 100% are reported by TeslaFi and can be plotted. As you can see it goes up and down without being influenced by weather, temperature, etc. I think it's just a function of the BMS state of calibration...
So in one year my battery has degraded by 8.6%, however it was only 5.5% last month. It gets worse then it gets better and then worse... I think the best thing is not to worry about it at this stage when there is 7 years warranty remaining...

 

[Adopado]

Actually, the miles available @ 100% are reported by TeslaFi and can be plotted. As you can see it goes up and down without being influenced by weather, temperature, etc. I think it's just a function of the BMS state of calibration...
So in one year my battery has degraded by 8.6%, however it was only 5.5% last month. It gets worse then it gets better and then worse... I think the best thing is not to worry about it at this stage when there is 7 years warranty remaining...

View attachment 707085

Have you been able to make any link between favourable phases of the graph and the patterns of driving/charging at that time or does it feel random and just as per your BMS calibration comment? I think I would go nuts trying to understand the patterns if I had a graph like that!

 

[MrBadger]

To be honest, I had thought that battery degradation was 'quick and easy' to assess by calculating the range at 100% charge using the current battery percentage and estimated range. Or does Tesla adjust the estimated range based on current ambient conditions to make that more difficult?

Its all very roughly estimated (a non exact science) by the BMS which can get inaccurate/drift. We just had our calculated amp hour capacity (CAC) reset, used to calculate range, and told to monitor things - hopefully it is just the BMS getting things wrong and nothing physical and over time the BMS can find a new normal. The only real way of knowing is doing some long drives at the reference consumption Wh/mile value.

 

[AAKEE]

Thanks for that!

So if I'm understanding that chart correctly, The 'best' option for minimising battery degradation out of the 4 scenarios I proposed is likely to be #1 (daily charge from 60% to 80%).

No, thats not right!

Its easy to draw the wrong conclusions when only reading one research report.
The results are very depending on which cycling schedule that is chosen.

From a lot of research reports we can be sure that these things are facts:
- Calendar aging might degrade the battery as much or more as cyclic aging. Most cars is used a few ours per day, during most of the rest of the day the battery is aged by time.
- The lower the SOC, the lower the calendar aging is. No exceptions as long as not below 0% SOC on the battery meter.
- Lower temps is god for calendar aging. When the battery is in use, 20-25C is goo
- The smaller the cycle( depth of discharge) the lower the degradation is.
- The lower the cycle is( ie the charging target) the lower the degradation is.

So, charge every day, not each other.
Use as low charging target as possible. Charge to 50% and arrive with 30% is better than charging to 60 or 70% and arrive with 40 or 50%.
Set the charge to start so the charging is done a relatively short time before starting to drive. If done so, the battery is at a lower SOC for most of the day.

I have a ‘21 M3P( Freemont, pana 82kWh).
I charge to 55-57% daily, use about 20-25% each day commuting to work. Charging is set( 11kW) to commence so it is ready about 1 hour before I go for work.
After 9 months and 23000km I still have full range om the battery meter and teslafi shows the same. The Nominal Full Pack value( via Scan my Tesla) is the same as when the car was new. Of course there should be a slight degradation but it is not seen by the BMS yet.
I have read, and have at least 30 research reports. A lot of reading, but this information sum up the things valid for Teslas/panasonic NCA cells:
How to preserve the battery

My plan seem to work:

Degradation from time( “calendar aging”) on panasonic NCA:
(Lesson learned: keep SOC low, and if possible battery from high temps during long time. High SOC together with high temps is not the best).

The difference between deep and shallow cycling. Lessons learned: shallow cycles at low SOC is better.

 

[GoodKarma]

Its all very roughly estimated (a non exact science) by the BMS which can get inaccurate/drift. We just had our calculated amp hour capacity (CAC) reset, used to calculate range, and told to monitor things - hopefully it is just the BMS getting things wrong and nothing physical and over time the BMS can find a new normal. The only real way of knowing is doing some long drives at the reference consumption Wh/mile value.

View attachment 707181

VanillaAir - how did you go about resetting your CAC?

 

[MrBadger]

VanillaAir - how did you go about resetting your CAC?

Tesla remote diagnostics took it upon themselves to do in response to a query I had about displayed range.