Help understanding my battery pack

[derichio02]

Hey All,

I purchased my 2020 MS Performance in Dec of 2019. At that time 90% charge was 307 so 100% Should be 341 out of advertised 348. Currently 90% is 300 miles and Anyway this is not what this is about 334. I’ve lost some mileage after 8k miles... whatever right... use percentage. I do use percentage and I’m also on a bit of a tangent because this is not what this thread is about.

I need help understanding my latest trip because I seem to be having a brain fart. I charged to 90% this morning and I arrived home with 20% after driving around 176 miles. So basically I used 70% of the pack. Fine. But then I took a look at my kWh and I see that I used 57kWh. So the assumption is made that 70% of my battery uses 57kWh. Well if that is the case then 57(kWh) / .7(70%) = Total kWh available or total battery capacity. Well that would mean that my battery capacity is approx 81.42kWh. I have to be wrong here and hope I really am have a brain fart...

Any help is appreciated

 

[kev1n]

sounds normal, 20% loss for HVAC/speeding/etc. also you lose range if you have the 21's

the reality is that youre not going to get rated miles unless you drive like a granny. you have to get under 300wh/mi

 

[derichio02]

sounds normal, 20% loss for HVAC/speeding/etc. also you lose range if you have the 21's

the reality is that youre not going to get rated miles unless you drive like a granny. you have to get under 300wh/mi

I completely understand that and I’m really asking a different question. If my division holds seems like the total capacity of my battery is 81kwh. I used 57kWh over 70%. If we think about the long range battery being 100kWh then 70% of that is 70kWh. Even if there is a 2% cap that some mention then 70% of 98kWh is approximately 68kWh. I’m using 57kWh when depleting 70% of my battery meaning I have a 100kWh battery capped at 81kwh if I am thinking about this correctly

 

[derichio02]

Searched around but didn’t find much info. Any local battery gurus to help my understanding?

 

[Greg29]

I can't answer your question but notice you took multiple trips since your last charge opening up the possibility energy was lost between trips. Perhaps try same experiment with a nonstop?

 

[derichio02]

I did have sentry mode enabled but wouldn’t and energy used be captured in the total kWh usage since last charge?

 

[ucmndd]

I did have sentry mode enabled but wouldn’t and energy used be captured in the total kWh usage since last charge?

No. that energy used display in the trip meter only reflects consumption when the car is moving.

 

[Alysashley79]

Have you noticed your kWh since last charge never matches the amount of kWh charged. Ie. my cars shows 41kwh used but when charging is done it replaces 49kwh.

 

[bluestreak]

I am a bit confused by the thread. If you can trust the car's info feed, and the battery drops from 90% to 20% and it shows 57 kWh drawn out of the battery, then the car is telling you that 70% = 57 kWh so 100% (useable) = 57/0.7 = 81.4 kWh. It seems to me that doesn't matter where those electrons went, that is what came out of the battery, so the software "thinks" that the useable battery capacity is 81.4 kWh. When I have done similar calcs on my P85D I have come out with around 76 kWh which is as much as I can get out of the battery, so at 0.200 kWh/km I should be able to do 380 km which is pretty much exactly what the "typical" kms predicts at 100%. Was the battery ever able to deliver 85 kWh? Seems unlikely. Typical 100%SOC kilometres has been steady for a couple of years in that 375-380 km range so not degrading at any noticeable rate, although 76/85 = 89% or 11% degradation if you assume 85 was really possible when new.

And re post immediate above, batteries are never 100% efficient, takes a lot more than 100 kWh in to see 100 kWh in the batteries, there is some "spillage" - inefficiencies, heat generation, running pumps and coolers while charging which "probably" (i.e. I don't know for sure) gets counted in the kWh added number.

 

[derichio02]

I am a bit confused by the thread. If you can trust the car's info feed, and the battery drops from 90% to 20% and it shows 57 kWh drawn out of the battery, then the car is telling you that 70% = 57 kWh so 100% (useable) = 57/0.7 = 81.4 kWh. It seems to me that doesn't matter where those electrons went, that is what came out of the battery, so the software "thinks" that the useable battery capacity is 81.4 kWh. When I have done similar calcs on my P85D I have come out with around 76 kWh which is as much as I can get out of the battery, so at 0.200 kWh/km I should be able to do 380 km which is pretty much exactly what the "typical" kms predicts at 100%. Was the battery ever able to deliver 85 kWh? Seems unlikely. Typical 100%SOC kilometres has been steady for a couple of years in that 375-380 km range so not degrading at any noticeable rate, although 76/85 = 89% or 11% degradation if you assume 85 was really possible when new.

And re post immediate above, batteries are never 100% efficient, takes a lot more than 100 kWh in to see 100 kWh in the batteries, there is some "spillage" - inefficiencies, heat generation, running pumps and coolers while charging which "probably" (i.e. I don't know for sure) gets counted in the kWh added number.

That exactly my thinking. I was hoping I was wrong. I’m going to do a more steady run to see if this theory holds.I would be hard pressed to believe that I have a 100kWh battery that has only 81kWh usable after 8000 miles and only supercharged 4 times and daily charge at home. This seems much worse thank my model 3 over 30k miles