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Are you sure Tesla says "as much as possible". Have you checked the Owners manual which can be accessed via the Tesla App for the actual instructions?
I been down this rabbit hole with our LFP Teslas
If you do not charge to 100% often BMS can be out with LFP's
Battery itself happier not living high or low.
Had Tessie since got both M3 and MY both LFP's and noticed it started dropping.
Happened after I started charging only 21kw at a time(in free 3 hours) and every 2-3 weeks to to 100%
So got Scan My Tesla and it said the same
So did a couple of 10%-100% chargers to get BMS back
Went from 57kw to 58.8kw on Scan My Tesla.. It moves depending on what the charge was.
The Battery itself is whatever it is.. just BMS does not show it flat like it does for NMC type cars.
MY shows it better it dropped down while I was doing shorter chargers then back up now as you can see below
If you do not charge to 100% often BMS can be out with LFP's
Battery itself happier not living high or low.
Had Tessie since got both M3 and MY both LFP's and noticed it started dropping.
Happened after I started charging only 21kw at a time(in free 3 hours) and every 2-3 weeks to to 100%
So got Scan My Tesla and it said the same
So did a couple of 10%-100% chargers to get BMS back
Went from 57kw to 58.8kw on Scan My Tesla.. It moves depending on what the charge was.
The Battery itself is whatever it is.. just BMS does not show it flat like it does for NMC type cars.
MY shows it better it dropped down while I was doing shorter chargers then back up now as you can see below
Max Spaghetti
Member
Interesting. I don't have Tessie, but I recently got SMT.
Here is a screen shot when I intentionally took my battery down to 0% recently (on the screen - it was actually 0.48% SOC according to SMT).
You can see that my Nominal Full Pack (which I think is what Tessie is reporting in your chart) is now at 58.4kWh. I think it was 58.0kWh a couple of days before - I had since charged to 100% and then I ran it down to 0% and then back up to 100%, so it improved a bit. It is still saying 58.4kWh after the 2nd 100% charge, but I'm going to do a few more 100% charges and see if it changes any further. The Nominal Full Pack (which is an estimate of degradation) determines the displayed km range at 100%. So my degradation figure (off the bottom of the photo) is currently 3.1% - calculated from 58.4 vs 60.5. It was 3.5%, so as you have pointed out, some of that degradation was temporary, so not real degradation.
The other factor that the BMS estimates is the Energy Buffer: you can see that mine is 5.75kWh. The energy buffer is the estimated amount of charge remaining when the display reads 0%, but plays no part in the estimated km range at 100%.
The Energy Buffer should read (I think) about 2.7kWh (4.5%) when everything is fully calibrated, so mine is more than double that. It reached 7.3kWh at one point which is why I decided to do some 100% charges to get it down again (I wasn't so concerned with the Nominal Full Pack/Degradation figure). I will be interested to see if some more 100% charges reduce the figure further.
You can also see that at 0%, SMT says that Nominal remaining is 6kWh, and Cell Volt Min is 3.172V - this is well above the 2.5V minimum cell volt for an LFP battery, so there is still significant charge remaining, but it is difficult to determine exactly how much (but it is likely at least 10%/6kWh based on that cell voltage). It might have helped the BMS if I had let it sit at 0% for a couple of hours, but it was time for bed so I declared the experiment over and just plugged in the charger...
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@Max Spaghetti I agree not sure I take it all the way to 0% I did a couple low 10's to 100 in a row as a few days of long trips in the M3
Then did a 10% to 100% in the MY both improved.
Unlike friends with NMC batteries yes it moves a lot more on Scan My Tesla.
I expect hover around 57-58kw next 100k on odo looking fleet avg
I did a couple low 10's to 100 in a row as a few days of long trips in the M3Then did a 10% to 100% in the MY both improved.
Unlike friends with NMC batteries yes it moves a lot more on Scan My Tesla.
I expect hover around 57-58kw next 100k on odo looking fleet avg
Max Spaghetti
Member
I stayed close to home at 3% doing some laps down to 1% then put the car in defrost mode down to 0%. I was also keeping an eye on Cell Volt Min. Can’t advance science without taking some risks haha!not sure I take it all the way to 0%
That might be so under a zero load situation. However when the battery is under load it might not be able to deliver the residual kWh because when you press on the accelerator the motor demands a certain amount of current and cause the battery voltage of some cells to drop below cutoff. A scenario would be driving on the flat and you have enough kWh to make it but then you need increased power to get off the highway via an uphill off ramp -the car stops even when there is residual kWh
So an energy buffer "usable" kWh might not be as accurate as we would like. Additionally the accuracy deteriorates over time due to battery degradation
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Max Spaghetti
Member
Yes indeed - and that is an important point when playing with fire.
At the time of the photo it was actually still under a load of 5.83kW (see top part of photo), as I still had defrost running at max (I stopped it after I took the screenshot).
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Max Spaghetti
Member
Just to report back from my experiment:
Charging from 0 to 100% did not improve the energy buffer significantly (I think it went to 5.6kWh).
However, after driving down to about 50%, one further charge to 100% restored the energy buffer to 2.6kWh (normal). This time I let had it sleep at 100% for a few hours before preconditioning and driving (which I hadn't done either before or after the previous 0-100% charge). It may be an important step to do this, to allow the BMS to get an accurate calibration, I'm not sure. But anyway, it worked, and my calibration is back to new. (And the degradation figure is still at 3.11% which is about where it should be after 12 months).
A week of driving since then (only charging to 67%) - and the figures have stayed put (2.6kWh buffer, 3.11% degradation).
My conclusion:
As expected, not charging weekly to 100% does not hurt the battery in any way, but it may gradually reduce the km driven before display indicates 0%. It may take 1-3 charges back to 100% and maybe a couple of hours sleep at 100% to restore the range back to where it should be. Without a scanning app you won't have any way of knowing this.
I plan to keep on doing what I'm doing (charging normally to 67%, and charging to 100% from time to time when I need to), and will continue to watch the data and report back anything new I discover. The only change I will make is that when I charge to 100% I will try to let it sleep before preconditioning and driving. Usually in the past, I would set a 100% target with a preset departure time and preconditioning. The trouble with this method is that the car does not get to sleep at 100%. I don't know for sure how important this step is (if at all) - it is based on a single anecdote.
I wouldn't be surprised, because with the nickel chemistry batteries it appeared that the BMS needed the car to sleep some times to get an accurate read on the cell voltages with the high voltage contactor open.
Driving immediately after charging and charging immediately after arrival does not allow the BMS to accurately measure the cells voltages.
I facilitate this by using scheduled departure with offpeak charging finishing about 1hr prior to departure.
I especially also do this when I get the opportunity to discharge the battery to a low SoC< 20%, or after charging to 80-100%. I select 1 hr only because I don't know exactly when the HV contactors open after the car is locked.
I don't fuss If I don't get the chance to let it sleep for 1hr - there are enough other charging sessions where it does occur. No need to do it every session.
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