Hi All. Some mornings when I unplug my car, my battery has lost charge from the end of charging to my departure. For example: I set my battery to charge to 70% SOC with departure at 7:30a. Precondition is on but only on weekdays. Today (Saturday), I unplugged my car at 11:30a and my batter SOC was 64%. Under the energy tool, it shows 6% of battery was used for vehicle standby since last charge. Sentry mode is off, cabin overheat is off, I do not use any third party apps, I did not open the Tesla app all morning, and precondition should have been off since it was a weekend. What is drawing down the battery during this time while plugged in? Is it normal? I would expect the battery to stay charged to the set SOC if it remains plugged in. Thanks for your feedback!
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Very normal.
We tend to think of battery energy like a fluid in a gas tank. That it shouldn't disappear unless used. But that energy is stored as chemical reaction not a quantity of substance. As the temperature of the battery changes, the ability of the battery to discharge that energy changes. The effect you're seeing is due to the battery cooling down. If you heated the battery back up, the "lost" energy would return.
AlanSubie4Life
Efficiency Obsessed Member
Right now there are huge BMS adjustments that can take place, even if the temperature does not change that much. See other recent threads documenting this.
Sometimes it will go up too. This increase is visible on the plot, but will not be tracked properly on the park losses subtotal tab.
In general these adjustments are nothing new, but will vary based on software version. And they are much more visible with the new tracking of standby drain and the new Energy screen tabs.
This is one of the reasons vehicles do not end up at the charge limit. For example my car lost 8 miles overnight after charging, last night. No actual losses occurred of course.
At 57 degrees of course temperature could be a factor as well, but this will also occur with a battery at a fairly stable temperature. (For example in my case the car may have warmed as it charged then cooled down a bit in the garage afterwards.)
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AlanSubie4Life
Efficiency Obsessed Member
This is not likely the issue unless the user is right next to the car and it is deciding to wake up all the time (which is not a given and not even sure it is a thing). It is very well documented that a sleeping car makes large BMS adjustments with no app interaction at all.
For me, this up or down recalculation happens when the battery changes temperature. If the battery is cold, and I drive somewhere where it's sunny, and the battery is warmer, then the chart shows higher when I come back to the car. More often, the battery gets colder, and it will show lower, when I come back to the car.
AlanSubie4Life
Efficiency Obsessed Member
Or you take the car from a warmish 65 garage, drive it to work and sit in 55 degree temps, running sentry for 9 hours, and don’t lose any charge to Sentry Mode per the Energy Screen tabulation (presumably because the BMS adjusted upwards (due to temp reduction, or just the change in SOC on the drive) to offset just enough any Sentry use (4-5 miles?), and it can’t display negative numbers so has no choice but to zero everything out).
YMMV
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