Rapid drain ONLY when low battery.

[kkl1993]

Hello, I was wondering if anyone experienced what I am experiencing with my Model S. I bought a used 2018 Model S 75D back in June 2020. It had 25k miles on it and the battery seemed to be fine. My 100% max capacity was 245 when it got delivered, but it seems to level out at 230 miles now at 100%, but whatever.

Anyways, I usually charge my car to 80% max. I have no issues with rapid drain then or even when it's at 50%. My car would lose maybe 1-2% in a span of 6-12 hours when not used. But when my car gets to around 20% battery life and not being used at all, the drain is ridiculously fast. My car was parked in a garage at 70°F weather outside with no sentry mode and no 3rd party apps connected, but it went from 38 miles left to 23 miles left in a span of 2 hours. I wanted to see how much farther it would drain but didn't want to damage the battery so I charged it. Has anyone run into this issue? Thanks in advance.

 

[ATPMSD]

You can try to calibrate the Battery Management System:

1. Drive the car down to between 5-9%
2. Let it rest for 3-hours
3. Charge to 100%
4. Let it rest for 3-hours
5. Drive the car down to below 95%

You may need to repeat this 2-3 times.

 

[serendipitous]

When your BMS gets a chance to sleep and measure the pack at low voltage, it re-calibrates its estimate of max and current energy. It's likely that you didn't "lose" capacity, but your BMS decided it had been too optimistic in the amount of energy remaining based on its earlier calibration. This will be more common if you rarely give it a chance to sit around and get measurements at lots of different states of charge. If you had just finished a drive when you parked it with 38 miles left, and the battery was warm, it will also "lose" capacity in this estimate as the pack cools down. This is also more noticeable at a lower state of charge because it's a higher chunk of your remaining capacity.

 

[ucmndd]

This is common with recent firmwares, I see it a lot in my S75. If I park my car with less than ~20% battery, it “loses” about 5% in the first hour or so after it’s parked. It doesn’t keep draining - it stops after that and holds steady.

Then charging will start, it will charge to my set limit, and then at some point after that the “missing” 5% comes back, giving the impression the car charged past the set limit by 5% or so.

I’ve written it off as harmless. I don’t think it’s anything to worry about.