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How often do you charge to 100%?
- Thread starter Black/Black MS
- Start date
boonedocks
MS LR Blk/Blk 19”
The only time my P85D has ever been charged to 100% is before a long trip and only then never left for more than a few minutes after hitting fully charged before leaving.
Except....the other day before I picked up from Service. My adviser asked if I wanted them to charge it since it only had 116 miles. I said, yes, that would be nice...except that they raised the charging limit from 90 to 100% and charged it full and left it like that for hours.
It's the first time in its entire life where it sat for more than a few minutes fully charged. Their reasoning for doing so is that I live 130 mile away and they thought I'd want it fully charged
Except....the other day before I picked up from Service. My adviser asked if I wanted them to charge it since it only had 116 miles. I said, yes, that would be nice...except that they raised the charging limit from 90 to 100% and charged it full and left it like that for hours.
It's the first time in its entire life where it sat for more than a few minutes fully charged. Their reasoning for doing so is that I live 130 mile away and they thought I'd want it fully charged
Time spent at high charge voltage is what causes dendrite growth and thus capacity loss. The less often you get your cell above 90%SOC the longer your battery will last. The below chart isn't specific to Tesla batteries, but the basic principle still applies. To extract the most energy out of the battery over its life time the best bet is to cycle it between 75% and 65%. This is not practical though, but widening it to 75%-25% (50% total battery capacity) will still get decent range and really dramatically improve the lifetime of the battery.
Compare the 75-25 and the 100-50 lines below. Same amount of energy used, vastly different lifetime results.
Obviously this is not practical all the time, but keep it in mind when you are planning your overall charging strategy.
-Jim
what is a DST cycle in terms of miles for a typical Tesla?
Interested in this as well. If the DST (which stands for dynamic stress test) cycle is basically equivalent to a full discharge/recharge cycle for a typical Tesla (so 250-300 miles depending on battery size) then over a 3 year lease you are only getting to about 150-180 cycles which is way over on the left of the graph where all the lines are basically on top of each other. To get to 5,000 cycles where the lines are meaningfully separating you would be at 750,000+ miles.
kingjamez
Member
sdorn is right. DST is Dynamic Stress Test and is intended as a rough equivalent to discharging while driving. The number of miles depends on the total amount of SOC reduction. For simplicity sake, if 100% battery gives you 300 miles, then the 50% SOC lines would give you 150 miles. 100->50 and 75->25 will both give you the same number of miles.
For most people, I think it reasonable to think in 100-150 mile cycles as that is longer than many people drive in a single day.
-Jim
whttiger25
Member
If you are worried about long term battery life, I would just set your daily charge to 75-80%, and charge more when you need it. If you are a little less worried, set it to 90% daily. Only charge to 100% before a trip, don't leave it there for more than a few hours, etc etc...
Done, shall we move on?
Done, shall we move on?
charging to 100% is not the issue as long as you do not let the car sit at 100% soc for an extended amount of time. I charge to 100% as often as I need that level of range. there are threads discussing this and people with cars that have high miles and regularly charge to 100% have noted little if any ill effects from charging to that level.
If looked at the total miles as a percentage for each to get to 90% of capacity. The one that produces the most miles is the 75-25 cycle with an estimate of 371,925 miles on an 85D. The 75-45 is a close 2nd at 369,360 miles. Interestingly, the 75-65 is the 3rd lowest at only 218,025 miles. This tends to back up the theory that a lower state of charge is best. It also debunks the theory that smaller charging increments are better. I would like to see a line for 50-25%.
I used 270 rated miles at 95% capacity (assumed half way wear point) with the swing in percentages, and estimated the cycles to get to 90% capacity based on the chart.
I used 270 rated miles at 95% capacity (assumed half way wear point) with the swing in percentages, and estimated the cycles to get to 90% capacity based on the chart.
whttiger25
Member
I don't think that's how the chart works? i.e. 75-65 isn't considered a cycle, it's considered 1/10 of a cycle...
gabeincal
Active Member
As I understand, sometimes it's actually beneficial to the battery to fully fully charge it because it balances the cells.
kingjamez
Member
Nope, each charge->discharge "set" is a cycle so from 75%->discharge to 65%->charge to 75% is one cycle.
-Jim
gabeincal
Active Member
So then another factor to look at is the number of miles you get out of a cycle...
kingjamez
Member
All of this reinforces the fact that it is basically meaningless over the life of a 45,000 mile three year lease. For longer term owners, according to the U.S. Department of Transportation Federal Highway Administration the average American driver logs 13,476 miles each year. That means you are at almost 15 years of driving just to hit 200,000 miles for the average American.
kingjamez
Member
Great analysis! Me too, but I'd bet the difference between starting at 75% vs. 50% is not that great. There actually may be some loss due to the fact that batteries heat up more (with same power output) the lower their SOC is. It would be an interesting number though.
Kinda... for somebody who doesn't really care like a lease owner, then yes they don't need to worry about this at all. However, I'd bet that even within 45000 miles you'll see appreciable degradation if only using the car from 100->80 and charging every day. Not enough to matter over 3 years, but it will make a big difference for the follow on owners.
The only caveat here is that I don't know what Tesla considers 100%? Does the Tesla BMS actually charge to 4.2V? I drive a leaf while waiting on the Model 3 and Nissan only charges to 4.15V/cell. If Tesla makes their 100% really 90% then the degradation effect of charging to 100% reported would be even less.
-Jim
I think this is the more relevant question, and one that I don't think I've ever seen anyone on TMC answer with any sort of evidence-based response. I think the article below and the chart pasted below provides some insight, but the smallest increment of time it uses is 2.1 months of sitting at 100% SOC. I don't know that there is any research out there that looks at damage that may be caused by allowing a vehicle to sit at a 100% SOC for less than 12 hours a few times per month.
Calendar Aging of Lithium-Ion Batteries
Several people have written that the size of the charge/discharge (i.e. 90-10 versus 90-70) is a very important, if not the most important factor in battery life. The chart does not bear that out because the smaller swings do not lead to more mileage out of the battery. As Dahl says in his talk, the SOC seems to be the most important factor (he also says temperature, which the chart kept constant). I will continue my practice of keeping the battery between 20% and 40% most of the time, with higher charges for trips.
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