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I reiterate what I've said before: what's best for the battery, and what allows the car the most accurate range estimate, may not always be the same.
The further to the "endpoints" you push your charge & discharge, the more data points the range estimation algorithm has to sample from. It may also allow for some additional range from balancing.
But, there's significant evidence (including some quotes from Elon) that the shallower your charge/discharge cycles, the better for the battery.
So, if you don't need the range, I hesitate to say that arbitrarily charging to a higher percentage just to see different numbers on the dash is a "good" thing...
The further to the "endpoints" you push your charge & discharge, the more data points the range estimation algorithm has to sample from. It may also allow for some additional range from balancing.
But, there's significant evidence (including some quotes from Elon) that the shallower your charge/discharge cycles, the better for the battery.
So, if you don't need the range, I hesitate to say that arbitrarily charging to a higher percentage just to see different numbers on the dash is a "good" thing...
For some people it saves $thousands$ in psychoanalysis, so while maybe not best for battery, you've got to factor in the other impacts
It doesn't seem like just range estimates (although I didn't drive it until it stopped, I drove to 13 rated miles remaining), it's real range regained presumably due to pack balancing. So the problem is that when you do need the range (as I did last month) you can't just get it back instantly.
We don't have any reports of significant degradation due to charging to a high state of charge. With the numbers out there, we would have data for sure by now. on the other hand, we do have plenty of reports of decreasing rated range due to charging to a low state of charge - not true degradation. Feel free to charge anyway you like, but at this point we have fair data to support charging to 90% routinely without meaningful negative consequences.
As many have pointed out here, I have to agree that balancing does not have to happen at 100%, but a post on the My Nissan Leaf forum helped me think differently about battery balancing. This is the brainstorm (so not perfect by any means):
I'm starting to think that the BMS computer doesn't necessary decide to balance the batteries at a specific SOC (90%, 100%). I think it has more to do with how it recognizes an imbalance in the batteries. So it is possible that the batteries can balance at any SOC. However, the higher the SOC the easier it is to recognize smaller imbalances between cells. I'm wondering if it is even necessary to charge to 100% more than once to initiate full balancing. Maybe once the BMS has identified the imbalanced cells/modules at 100%, it will continue to balance until its done, even if the car remains at a lower SOC afterwords. In fact once a range charge has finished and the imbalanced cells have been marked, it might take several days or weeks - again at a lower SOC - to balance these marked cells. So what looks like effective balancing because of multiple 100% charges is actually charging that occurs over a long period of time from the first 100% charge. Information from the battery tear-downs on this forum show how the shunting hardware can only draw a small amount of power at one time, hence the long period of balancing. Charging to 90% helps the BMS identify imbalanced cells/modules, just not with the same resolution as at a 100% charge.
I'm starting to think that the BMS computer doesn't necessary decide to balance the batteries at a specific SOC (90%, 100%). I think it has more to do with how it recognizes an imbalance in the batteries. So it is possible that the batteries can balance at any SOC. However, the higher the SOC the easier it is to recognize smaller imbalances between cells. I'm wondering if it is even necessary to charge to 100% more than once to initiate full balancing. Maybe once the BMS has identified the imbalanced cells/modules at 100%, it will continue to balance until its done, even if the car remains at a lower SOC afterwords. In fact once a range charge has finished and the imbalanced cells have been marked, it might take several days or weeks - again at a lower SOC - to balance these marked cells. So what looks like effective balancing because of multiple 100% charges is actually charging that occurs over a long period of time from the first 100% charge. Information from the battery tear-downs on this forum show how the shunting hardware can only draw a small amount of power at one time, hence the long period of balancing. Charging to 90% helps the BMS identify imbalanced cells/modules, just not with the same resolution as at a 100% charge.
As an interesting follow up to this discussion, my rated range has been creeping upwards over the last few weeks.
I've previously advocated that unless needed, opting to charge/discharge to greater extremes just for the sake of the algorithm having a greater sampling range[1] and thus providing a slightly higher estimate isn't worth the potential impact to the battery health. As such, I've continued to charge to 70% during the weekdays, typically only discharging to 30-40% or so.
I'd typically see about 171 miles @70% for the previous several months. It crept up to 172 about 5-6 weeks ago. It jumped to 173 a bit back, and this morning I had 174 miles of estimated range at the same 70%.
I earlier had surmised that a couple of miles of range estimate variance could likely be due to a number of factors, including temp, etc... I suspect that's what I'm seeing here.
[1] I do acknowlege that if one is in dire need of the few miles that full balancing might add, there's some value in allowing that to occur
I've previously advocated that unless needed, opting to charge/discharge to greater extremes just for the sake of the algorithm having a greater sampling range[1] and thus providing a slightly higher estimate isn't worth the potential impact to the battery health. As such, I've continued to charge to 70% during the weekdays, typically only discharging to 30-40% or so.
I'd typically see about 171 miles @70% for the previous several months. It crept up to 172 about 5-6 weeks ago. It jumped to 173 a bit back, and this morning I had 174 miles of estimated range at the same 70%.
I earlier had surmised that a couple of miles of range estimate variance could likely be due to a number of factors, including temp, etc... I suspect that's what I'm seeing here.
[1] I do acknowlege that if one is in dire need of the few miles that full balancing might add, there's some value in allowing that to occur
I made my statement in case you had Range Mode turned on for some of your comparisons. It can skew your results.
UberEV1
Member
Updated Data Point: Continued charging to 90% daily and rated range went up a bit more to 230. Then, for the first time in 6 months or so, did a full charge and got 256. This is roughly the same as I saw last time I did a full range charge. I would love to see those last two digits reversed (256 --> 265), but after 15 months of ownership perhaps this isn't so bad.
Fedderman
Original: 2012 Model S (85); Current: 2024 Model S
Did my first range charge today since changing to 90% charging a few months ago. My 90% consistently yields 231 rated, and today's range charge yielded 258 rated (both with range mode on). Used to get 265 when new, with range mode off. Car is 23 months old, with ~17k miles.
I guess my 60 is more efficient or something. 39k miles still get 176-178 on 90% and 196 at full. If I run the numbers that means you should be getting 249 at 90% and 277 at full. Just the percentages dividing my number by 60 then multiplying by 85. I was getting ready to get another MS, but if those are the numbers for the 85, I should just look for another 60 as I have never had a problem with range on my car. Just seems more efficient and cost effective.
FredTMC
Model S VIN #4925
Just celebrated my one year today. 90% been around 230-231 and range between 257-258. 24,381 miles as of this evening.
Fedderman
Original: 2012 Model S (85); Current: 2024 Model S
Assumptions must be off somewhere - 277 rated miles for a range charge would be 12 more than I got when brand new.
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