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Waking up to less than the set charge.
- Thread starter Hunt3r
- Start date
The battery percentage is just an estimate. The BMS cannot know precisely what quantity of energy the battery can hold "now", and cannot know precisely how much energy is held in it now. Those two uncertainties mean the "percentage full" is certainly uncertain as well 
I cannot explain all the principles of chemistry behind, and temperature might play a role in it. Suffice it to say that it's normal for the percentage to fluctuate a few points, in both directions, the morning after a charge.
I've had mine vary by up to 3 or 4 percent in both directions.
I cannot explain all the principles of chemistry behind, and temperature might play a role in it. Suffice it to say that it's normal for the percentage to fluctuate a few points, in both directions, the morning after a charge.I've had mine vary by up to 3 or 4 percent in both directions.
Nothing has changed since I've owned the car, and this is only happened the last couple days. I almost always wake up to 90, 89 on a rare once in awhile.
The battery percentage is just an estimate. The BMS cannot know precisely what quantity of energy the battery can hold "now", and cannot know precisely how much energy is held in it now. Those two uncertainties mean the "percentage full" is certainly uncertain as well
I've had mine vary by up to 3 or 4 percent in both directions.
All I can say is that's never been the case. It's almost consistently at 90, every rare once in awhile it'll be 89 if I don't get in the car first thing in the morning. That happens about as often as I come out and it's actually at 91.To have it dropping consistently day after day the last couple days is the first. Half the time I can get where I'm going with it's still showing 86. Lol. Typically it's set to 90, it charges until it indicates 90 and then it shuts off. For it to drop three or four or more percent just sitting in the garage for a short period of time seems excessive and unusual.
That number will not affect the distance you can cover... It's an estimate. The car charged to what it thought 90% would be. A few hours later it now thinks that your battery has slightly more overall capacity and with the energy that's in it, that now represents only 86%. As far as I know there's the same number of kWh in that battery.
alexcue
Member
I guess I'm lucky, I can charge at the office, so I rarely charge at home, Mine goes the opposite way, I set it for 80% and later TeslaFi shows it goes up to 82%. Now many times it will also go down by the time I leave from work (i can't set it for departure because others use the charger also, but since I'm first in I get first dibs) When it's especially hot the Cabin Overheat Protection kicks in wakes the car and this causes some drain especially if we are tickling the 100's
Yeah I can understand basic variances. But my driving situation is pretty consistent, and the car charges overnight in the garage so battery is cool, temperature is always consistent. And the charge state has been consistent for all the months we've had the car. It's just the last 3 or 4 days we've noticed a change. I think it started after the last software update so I'm wondering if something is running in the car that wasn't before. Or maybe it's waking up in the middle of the night. But I can't see anything obvious. Did a soft reset so we'll see if that changes anything. I may change the charge time so I can personally see if it's getting to 90 and dropping or not getting to 90 in the first place.
pepperoni
Member
Pretty common. Your car is just changing the estimated battery charge and capacity based on charge added, initial and final battery voltage, plus I’m sure a lot of other factors. My car frequently adjusts its % estimate after sleeping. I wouldn’t be concerned.
I'll just speaking from my experience of owning the car for the last few months, this is not common for us. Not remotely.
That being said I think it's been fixed. Few things, for starters I think during the software update or possibly inadvertently, it reset my preset charging time. So instead of it charging in the overnight prior to the morning, it was likely charging as soon as I plugged it in. Therefore it was sitting for 10 to 12 hours longer than it normally did after charging. Secondly I did do a soft reset, and toggle many of the related settings.
Since doing that earlier in the week, we seem to be back to normal. Charging set to 90% and waking up to precisely 90% consistently each day so far. We'll see if that continues to be the case, but so far I think we're back to our normal.
pepperoni
Member
I understand this hasn’t been your experience. I am just providing an explanation for what you experienced. There is nothing to “fix” here, this is just the way the BMS works from time to time.
I don’t suppose it is easy for the BMS to estimate exactly what battery percentage and range is left. It can’t just add up charges and discharges. These are relative measurements, and small errors will gradually integrate up to large ones. It can’t just look at battery voltage either, since this is affected by recent battery charge/discharge, temperature, and I’m sure a lot of other factors. Furthermore, battery degradation affects the calibration, so it will constantly need to recalibrate over days, weeks, months.
If you are also only charging to 90% and have the same driving pattern every day, you are giving the BMS a very limited set of data to work with, so the calibration may be fairly stable when it sees only a small amount of data. It may need to take larger recalibration steps when it sees something different. I’m just speculating here. What I can tell you for certain is that this is normal behavior, even if you haven’t seen this before.
But you refused to acknowledge that it's a normal thing, so you still think it was a "problem", so you will GET worried again as soon as it starts doing it again.
Lol. For me it wasn't normal so yes I questioned it. And this week it's been exactly the way it was Prior so normal is normal again. LOL I found a couple of possibilities, seem to be it.
I ran three errands today and came home with the same charge I was waking up to when this started. So yeah that was not normal for me.
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pepperoni
Member
You started this thread asking “any ideas why that would be?” Several of us answered your question such as me and @GtiMart and you essentially responded with a thanks but no thanks. Were you looking for a different answer? I’m glad your car is back to “normal” again, but I hope you remember this conversation and find it useful when your car behaves like this again. Because it will.
I said thanks because I appreciate the input but saying it's normal when it wasn't was not "any ideas". There was at least one setting that had been changed and the car was apparently staying 'awake' all night (maybe 8-10hrs) after the software update. The car is "Still" back to what was normal, iron clad and solid as a rock. In fact after losing power during the hurricane, it sat for 3+ days and still hadn't lost as much of a charge as it had on any one of those days. I'm not sure why it's so upsetting to some people that the issue is been corrected. I'd actually think that suddenly losing 5% battery charge in what should have been an hour or two while asleep in a climate controlled garage would be more of a surprise. I'm so glad mine isn't normal by those standards, it might not make it through the day.
(Didn't you just get yours in like April/May?)
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