The usual Battery Degradation Topic

[gtg465x]

I have touched the subject sometines.
It is easy to dig a whole that make the answer not very short and also get everlobg discussions about the base for the strategy.

Charging to 100% is not very bad, even for NCA or NMC.
The forum truth is to not let the car stand long time if charged to 100%.
While it is true that letting it stand at 100% cause more calendar aging/degradation than if it stands at 30% it is not at all catastrofic. In some cases 100% is less bad than 75-85%.
When being above a plateau, the degradation is more or less the same, unless in extremely high temperatures.

View attachment 900751
As we can se, it is about the same degradation above the “step”. And yes, the calendar aging hapoens even if we use the car, and for most people it isnot used for 22hours a day. The graphs above is valid for us and our EV’s!

The above in memory, 100% is not really worse than 70-90%.
That research report has a few years but we have no data telling us that new LFP is taking a lesser hit than before. Perhaps/probably the rate is slightly slower than in the chart but the basic principle probably still is valid.

I would charge to 100% once a week, but I would have it at lower SOC the other days, 50-70% depending on the minimum SOC covering my needs.
I would charge late (finished shortly before the drive).

We have some data, but as the LFP cars have a hard time judging the true SOC below 100% I would guess that its at least slightly harder for the BMS to judge the capacity as well, as different true SOC + the difference in energy in/ out is part of the calculation.

The charts for LFP’s at teslalogger.de show us that the LFP degradation is about the same or slightly less than other teslas (NCA mainly). We know the LFPs is non sensitive to large cycles and can do many of them so the degradation we see is more or less calendar aging only.


It probably is per above

Thanks! Solid info. I didn’t realize LFP wasn’t sensitive to large cycles. That’s good, because I drive my car very little, so my strategy has been to not charge every time I’m home, but just leave it at what charge it’s at until it get down to around 20-30%, and then just before the next time I need it, charge to 100% and repeat. This leaves me only charging to 100% about once every two weeks. Was wondering if I shouldn’t charge to 100% every time and only charge to 60% or 70% in between to reduce average cycle size.

 

[AAKEE]

Thanks! Solid info. I didn’t realize LFP wasn’t sensitive to large cycles. That’s good, because I drive my car very little, so my strategy has been to not charge every time I’m home, but just leave it at what charge it’s at until it get down to around 20-30%, and then just before the next time I need it, charge to 100% and repeat. This leaves me only charging to 100% about once every two weeks. Was wondering if I shouldn’t charge to 100% every time and only charge to 60% or 70% in between to reduce average cycle size.

LFP’s can handle thousands of 100-0% cycles, so that part is covered in any situation with LFP.

But the degradation from charge cycles is anyway (even with NCA or NMC) much smaller for more or less any EV than the calendar aging is, so saving on cycles in most cases increase the calendar aging if we compare to the option to charge often and stay low in SOC range.

Cyclic aging is neglible with LFP anyway.

 

[Paige111]

There is two types of degradation.
The first one is calendar aging which happens even if the car is not used.
Second one is cyclic aging, which comes from cycles( = driving + charging).

The calendar aging is the dominant part fort most Tesla owners for the first (at least) five years.
Calendar aging reduces over time( square root of time).
Calendar aging invreases with higher SOC and higher tempersture.

Cyclic aging most often reduces with increasing cycles but it depends on the cycles size and current. The easiest eay for us to see cyclic aging is as a fixed number per Equivalent Full Cycle or miles driven.

A new Tesla long range/performance probably loose about 5%* of the battery capacity during the first year if charged to 80% due to calendar aging, even if the car isnt driven at all.
An average driver perhaps cause a cyclic aging of about 1% during the first year.

*) The calendar aging is temperature dependent so the actual value will depend on the climate etc.

This is a graph (from one of many research reports on the subject telling us the exact same thing):

View attachment 778271

Check for the NCA-graph.
80% SOC cause about 5% if the ambient temp is 25C during 10 months. This will be about 5.5% on a one year basis according to the ”square of root formula”.

Calendar aging values:
After one year 5.5%
After two years 7.8%
After three. 9.5%
After four. 11%
After eight years 15.5%

Of course this wont be a exvation exact to the points.

For the batteries in the car the average temperature for the battery cells will be higher than the ambient temp. Charging, driving and hesting from the sun will cause this.

Mine has 11% loss in 18months -16K mls -Tesla says its normal -they wont help , Service dept refused to check my battery -said Id have to pay $245 to check it I have 320mls @100% started w/ 356mls 18months ago

 

[AAKEE]

Mine has 11% loss in 18months -16K mls -Tesla says its normal -they wont help , Service dept refused to check my battery -said Id have to pay $245 to check it I have 320mls @100% started w/ 356mls 18months ago

You’re in the LA area? (For knowing climate/Temperatures)

Is it a Model 3 LR?

How fo you charge it? To what state of charge, at what time of the day do the charging start ( = leading to how long the car is parked at high SOC).

Do you park it in a garage or always outside in the sun?

 

[seenhear]

Is the "nominal full pack" (NFP) capacity reported by Scan My Tesla an accurate measure of the battery's real capacity, or is it a value that is calculated and can drift if the BMS need "recalibration"?

Car is an Oct. 2017 Model S 75. I think NFP right now is around 63 kWh. I have noticed that the NFP number is not always the same.

I don't really care too much about the reported range. I use % SOC display. So I'm assuming that a 100% charge means the batteries have the kWh of the NFP capacity that SMT reports, and at 50% I'm at half that amount of kWh energy stored in the battery.

But if the NFP value drifts with reported range, then I would want to try one of these calibration methods, just to get a good idea of where my battery is in degradation.

 

[AAKEE]

Is the "nominal full pack" (NFP) capacity reported by Scan My Tesla an accurate measure of the battery's real capacity, or is it a value that is calculated and can drift if the BMS need "recalibration"?

It can drift.

True SOC is measured by cell voltage at rest /open contactors. Knowing true SOC and charging or discharging a measured energy (kWh’s), and then measuring the true SOC give us the possibility to calculate the capacity. For example if a charge increases the SOC with 50%, and the number of kWh “inserted” (this is a big simplification, but anyway) is 40kWh, the capacity should be 80kWh. The same for driving up 50%, if the number the battery outputted was 40kWh at a reduction of the SOC was 50%, the capacity is 80kWh.

My car was fairly off during the end of the last summer. But there is no better way except driving a 100% until the car stops and measure the energy that the batteri delivered.

Car is an Oct. 2017 Model S 75. I think NFP right now is around 63 kWh. I have noticed that the NFP number is not always the same.

I don't really care too much about the reported range. I use % SOC display. So I'm assuming that a 100% charge means the batteries have the kWh of the NFP capacity that SMT reports, and at 50% I'm at half that amount of kWh energy stored in the battery.

For my car, the nominal remaining have always gotten slightly above the nominal full pack. For example, NFP 81.6kWh got to 82.0kWh nominal remaining. This has been the same thing each time I have charged full.

But if the NFP value drifts with reported range, then I would want to try one of these calibration methods, just to get a good idea of where my battery is in degradation.

(You have SMT?)

I have found that its possible to interpret some things in for example teslafi.
If the nominal full pack is calculated to low, the calculated SOC when parking is lower than the real SOC. The car calculates the SOC when driving and updates is after a drive, measuring the real SOC. This is vice versa for overestimated battery capacity.
Same for charging, if the battery capacity is overestimated, the SOC will be slightly higher than the planned charging target as the number of kWh is calculated as exact SOC measurement cannot be performed during charging.

 

[Hiline]

Something we do know is that cycling depth is probably largely irrelevant for Tesla batteries as evident by many fleet teslas which like to do deep discharges and recharges to 100% in short amount of time which apart from the supercharger calibration issue leading to premature degradation due to charging beyond 100% doesnt significantly harm the battery.

What is the supercharger calibration issue?

 

[AAKEE]

What is the supercharger calibration issue?

Supercharging do not charge beyond 100%.

The 100% definition is cell voltage 4.200V
Any supercharger (or *any* charging session for that mather) will not deliver a higher cell voltage than 4.200V on each pack of cells. The highest reading cells will limit charging voltage so this is not overrun.

The standard for stopping the charge is when the charging current has dropped to a specific fraction of the set charging power (current). For example, 1/20 times charging current.

I have logged more or less all my charging sessions and also looked realtime (nerdy look ) with SMT when supervharging.
Never, ever was even 0.01V above 4.200.
Highest reading 4.200V.

There is no calibration issue for SuC charging to 100%.

If the BMS is of on either the actual SOC or the NFP, a calculated SOC target could be wrong, as the charges below 100% is calculated like “need to charge 30kWh to reach 70%. So in these cases, charging and the parking the car, the SOC number can change when the car sleeps, or rests.

But it won’t go above 100% true.
SMT can show 101%, but that is only a result of the nominal remaining going above the nominal full pack. 101% shown in SMT will not be more than 100% true SOC. Ever.