I am seeing weird fluctuations in my SOC on my 2022 MYLR. I start my day at 80% and drive to work. By the time I walk from the garage to the office (5 min) I open the app and I have lost 3-4%. Then, when I arrive home in the evening, I open the app 5 min later and I have gained 3-4%. Rinse and repeat this every day since I have been on 2023.12.x software. Last night I was looking around in service mode and noticed that in two different locations the SOC is stated differently. In one location it reads the same percentage as the top of the display reads. The other location was reading almost 7% higher. I am not sure if both of these locations are supposed to be the same. I would appreciate if someone could take a look on their end and see if it is the same. My assumption is that this is indicative of a software bug and nothing wrong with BMS or Battery. I have also tried to calibrate the BMS by running down to under 5% and charging to 95% a few times, but nothing changed.
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BMS or Software Issue?
- Thread starter DJ Avenger
- Start date
Over the recent weeks, I’ve noticed on some days the SOC would jump up/down. After some thinking, my thought at the time was that it was related to weather.
Specifically, we’ve been having fluctuating days, with pretty big temperature swings within the day. Now, it’s not just the outside temp, but the Tesla’s ability to heat/cool the battery.
Direct ambient temps affect the BMS’s measurements of the battery and the battery’s ability to provide power. Tesla’s heat pump system has to, as one of its many jobs, keep the battery at/close to an ideal temp when it can. Of course, the heat pump’s ability to do that is also affected by the outside temp. Combined with cycles between driving (when the heat pump is active) and not driving (where it’s turned off for the most part), that means measurements of the SOC can change.
At least, that’s what I thought at the time. Since then, I’ve simply stopped thinking about it.
*note: there was more, but it was a bit of a tangent, so I’ll end it here*
Specifically, we’ve been having fluctuating days, with pretty big temperature swings within the day. Now, it’s not just the outside temp, but the Tesla’s ability to heat/cool the battery.
Direct ambient temps affect the BMS’s measurements of the battery and the battery’s ability to provide power. Tesla’s heat pump system has to, as one of its many jobs, keep the battery at/close to an ideal temp when it can. Of course, the heat pump’s ability to do that is also affected by the outside temp. Combined with cycles between driving (when the heat pump is active) and not driving (where it’s turned off for the most part), that means measurements of the SOC can change.
At least, that’s what I thought at the time. Since then, I’ve simply stopped thinking about it.
*note: there was more, but it was a bit of a tangent, so I’ll end it here*
I've seen a pretty big difference between the SOC displayed in the car and the SOC displayed in the mobile app. It's been especially true in colder weather. One displays the pure state of charge of the pack relative to voltage while the other tries to estimate the amount of energy that you will be able to get out of the pack when driving. When the pack is cold, less energy can be extracted out of it. I've seen a difference of up to 7% in the worse colds. In the car it gets displayed in the battery details as a blue slice, to highlight the amount that wouldn't be available.
I realize that you're in Texas and you might not get cold enough weather for this but still, this is one reason why SOCs might not be the same when looking in different places.
EDIT: Another idea. Teslas charge to a real 100% (no buffer up top) but they do keep a buffer at the bottom. 0% SOC displayed is not 0% SOC relative to voltage. I suspect 33.7% is true charge whereas 26.8% is displayed SOC in the car in your screenshots. The buffer should be smaller than that though... have you taken the screenshots at the exact same time?
I realize that you're in Texas and you might not get cold enough weather for this but still, this is one reason why SOCs might not be the same when looking in different places.
EDIT: Another idea. Teslas charge to a real 100% (no buffer up top) but they do keep a buffer at the bottom. 0% SOC displayed is not 0% SOC relative to voltage. I suspect 33.7% is true charge whereas 26.8% is displayed SOC in the car in your screenshots. The buffer should be smaller than that though... have you taken the screenshots at the exact same time?
OxBrew
Active Member
I think the service mode SOC is not corrected for temperature, and the displayed SOC is corrected. So it will change a bit as the temps change.
The app can be minutes or hours out of date, so as the corrected SOC fluctuates, the app can be way out of sync.
The app can be minutes or hours out of date, so as the corrected SOC fluctuates, the app can be way out of sync.
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