I'm going to be a new M3LR owner in a couple of months. I'm trying to figure out the optimal charging profile. I've been reading this thread for hours and am more confused than ever. I had hoped there would be a consensus recommendation. Otherwise the car suggests '90%' 'daily'. Is this a good idea. Should it be charged back to 90% after each trip, no matter how short, or to let it go down further?
First of all:
Your battery will be fine without any special handling from your side. Thats the way Tesla have managed it. No need to be a battery engineer.
Teslas advice in short: Always connect the charging when possible. Only charge above 90% for longer trips. Thats it.
But this will not be the same thing as minimizing the degradation to a minimum. Teslas advice is aiming to make the EV owning easy.
I have written a lot of posts about this. If you would like to keep the degradation to a minimum, you can do that. No need to, but if you for any reason would like to, its possible.
Lithium ion batteries degrade from calendar aging and cyclic aging. For most, the calendar aging is the dominating degradation early in the cars life. Cyclic aging comes from the cycles.
Low SOC wears less on the battery. Calendar aging is least at low SOC and highest at high SOC.
Cycles wear less at low SOC. Also, smaller cycles wear less than larger cycles.
- Charge often. This will keep your cycles small.
- Dont charge to a higher SOC than you need. If you really need 90% each day, use 90%, or charge one extra time each day and use lower SOC. If you only need 50%, charge to 50%.
- If possible, charge close in time before using the car. This reduce the time the car stands with high SOC.
I have written a lot of posts with detailed description of the fundamentals behind the advice above, taken from a lot of research about lithium ion batteries. Do a search on my posts if you need more info.
But there is one issue that I think should be addressed: the difference in "percentage of capacity" used in published scientific experiments (which will be true, and presumably with a high and specified upper voltage limit) and the percentage displayed by the Tesla UI. I suspect 100% on Tesla is a bit less than 100% of science charge, but I'm not sure.
Is there any specific evidence on this, e.g. from cell voltage measurements on the car?
100% on the screen is 100% real SOC. The bransch standard for this type of lithium ion batteries is 4.20V/ cell = 100% and thats what Tesla also use. When you read 100% the cells will have 4.20V/cell. If you try to measure it, or as most people use Scan My Tesla, you will se 4.19x or something, but this is because the car always is on, using a little power when yo can check the voltage.
The charging stops at 4.20V/cell. I have a lot of ”evidence” for this, but at this point I think we can skip this part. Just trust me and the other ones that say so.
0% on the screen is 4.5% ”true SOC” of the capacity that Tesla calculates, those 4.5% is the buffer below 0% on the screen.
This is a map of my degradation so far, 14 months and close to 35.000km. I follow my advice above, charge to 55% daily and my charge setting charges just in time so most nights my car sit at 20-35%SOC. I havent really lost any range but the other cars of the same type (model 3 performance 2021) have lost 5% in average. My car has lost least of all.