Is this a sign of Battery Rebalancing?

[Ali’sMax]

I’m a little confused about battery rebalancing.
I have my X100D for over a year now at 16,000 miles mark. I make 2-3 trips a month to central coast, I’m in OC.
In the first 8000 miles I charged it to 80% in beginning of the week and let it go down to 50% before I charge to 100% for the trip. I don’t plug in car at all during the week and only charge at supercharging stations. I don’t drive much during the week, mainly using the car for long trips to central coast.
I started to notice that I don’t get as much miles for set %
I since then stopped my charging habits and plug in nightly set to 70% and charged to 95% before my trip
I noticed that at 70% mark my car usually ends up with 202-206mi and somehow phone app miles are different than actual car miles
It has been awhile since I made the trip to central coast(last trip was October) so I charged the car to 100% 286mi for the trip back and recharge car at 32mi back to 70%
This time phone app shows 197mi at 70% but when I get into the car it actually is at 216mi. I double checked the %bar thinking maybe my husband moved it but the bar is set exactly at 70% and the green color charge indicator went beyond the charge bar?
When I first got my car brand new 100% gives me 295miles do you think the car is rebalancing itself? Since now 100% gives me 186miles it’s 3% difference. So do you think the car is rebalancing itself when set to 70% should give me 206miles assuming no degradation but I end up with 73% at 216 miles?

 

[Big Earl]

Only charging to 70% can cause the state of charge calculation to become inaccurate. Somewhere between 80 and 90% daily seems to be the ideal balance. I'd recommend running it down to between 10 and 20% and charging above 90% for several charges in a row to retrain the calculation.

 

[ajdelange]

No, I don't think reballancing is responsible for what you are seeing. Reballancing is going on all the time behind the scenes and uses complex algorithms within the BMS. I think it is just normal variation in estimates of the battery capacity that are calculated after each charge session.

If you think your car was good for 295 miles when fully charged with an undegraded battery then at 70% charge you should have 0.7*295 = 206.5 miles of range and at 73% charge you should have 0.73*295 = 215.4. As you see 216 at 73% charge you are actually a bit ahead of the game. After 16,000 miles your battery has not degraded at all - as indicated by this single data point. Your assessment of battery degradation should be based on looking at historical charging data. To do this manually is a big pain so, naturally, someone writes an app to automate the process. There are a couple. I, and many others here, use TeslaFi. It gives you a battery report that looks like this:

My picture isn't very interesting as I haven't had the car long. Nevertheless it shows the estimated 100% range as calculated at the end of each charge and how those charges were distributed over distance driven.

TeslaFi collects other neat data from your car (which increases the apparent vampire drain) and they also collect $50/yr from you for storing it etc.

Another thing that may be confusing to you is that there are two kinds of range: rated range and estimated range. Rated range is based on the assumption that your car uses 100000/295 = 338.98 Watt hour for each mile you drive. Thus if the battery us 73% charged it hold 73000 Watt hours of energy and would be expected to travel 73000/338.98 = 215.4 mi. 338.98 is determined from a specific set of driving conditions and, clearly, does not always pertain in the actual conditions you are driving under. In a headwind on positive grade when it is cold and raining you can use substantially more. Going generally down hill with a tail wind on a warm day you will use substantially less. To account for this the car computes your actual consumption from the last 5, 15 or 30 miles and computes a second estimated range based on that. Be sure you know which range you are looking at.

Finally, as to why the car is charging beyond the set limits - that's a mystery. One possible explanation is that it charged to 70% (70 kW) while cold and then things warmed up. A warmer battery holds more energy than a cold one because while it contains the same number of ampere hours its voltage will have gone up. That thesis seems a bit of a reach, though, as the BMS knows that the temperature of the battery will be brought to within a certain range within the first few miles of driving.

 

[Ali’sMax]

No, I don't think reballancing is responsible for what you are seeing. Reballancing is going on all the time behind the scenes and uses complex algorithms within the BMS. I think it is just normal variation in estimates of the battery capacity that are calculated after each charge session.

If you think your car was good for 295 miles when fully charged with an undegraded battery then at 70% charge you should have 0.7*295 = 206.5 miles of range and at 73% charge you should have 0.73*295 = 215.4. As you see 216 at 73% charge you are actually a bit ahead of the game. After 16,000 miles your battery has not degraded at all - as indicated by this single data point. Your assessment of battery degradation should be based on looking at historical charging data. To do this manually is a big pain so, naturally, someone writes an app to automate the process. There are a couple. I, and many others here, use TeslaFi. It gives you a battery report that looks like this:

View attachment 377846
My picture isn't very interesting as I haven't had the car long. Nevertheless it shows the estimated 100% range as calculated at the end of each charge and how those charges were distributed over distance driven.

TeslaFi collects other neat data from your car (which increases the apparent vampire drain) and they also collect $50/yr from you for storing it etc.

Another thing that may be confusing to you is that there are two kinds of range: rated range and estimated range. Rated range is based on the assumption that your car uses 100000/295 = 338.98 Watt hour for each mile you drive. Thus if the battery us 73% charged it hold 73000 Watt hours of energy and would be expected to travel 73000/338.98 = 215.4 mi. 338.98 is determined from a specific set of driving conditions and, clearly, does not always pertain in the actual conditions you are driving under. In a headwind on positive grade when it is cold and raining you can use substantially more. Going generally down hill with a tail wind on a warm day you will use substantially less. To account for this the car computes your actual consumption from the last 5, 15 or 30 miles and computes a second estimated range based on that. Be sure you know which range you are looking at.

Finally, as to why the car is charging beyond the set limits - that's a mystery. One possible explanation is that it charged to 70% (70 kW) while cold and then things warmed up. A warmer battery holds more energy than a cold one because while it contains the same number of ampere hours its voltage will have gone up. That thesis seems a bit of a reach, though, as the BMS knows that the temperature of the battery will be brought to within a certain range within the first few miles of driving.

Thank you so much for your explanation.
I’m just glad that my battery didn’t degrade too much since I didn’t really understand the idea of plug in even though I have sufficient battery juice in the first half year of owning the car.
So I made another trip to central coast and this time start charging at 23mi to 75% and phone app notification shows done charging at 211mi around 1am but checked on tesla app itself this morning at 6am it shows 230mi?
It’s pretty cold this morning in the mid 40’s, I’m still confused why app’s miles don’t correlate with actual car miles
But happy that battery seems to be doing ok even though if I charge to 100% it does not give me 295mi when brand new