I charge to 90%. When my car finishes charging, the app says how many miles it has when it stopped charging. I always let the car sit, without waking it up, at least 3 hours after it is done charging. Sometimes the # of miles remaining is higher when I get in the car than what the app stated it stopped at. What mile # should we look at when calculating how many miles we have lost?
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How I Recovered Half of my Battery's Lost Capacity
- Thread starter SomeJoe7777
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- battery degradation Range
AlanSubie4Life
Efficiency Obsessed Member
Miles extrapolated (as little as possible extrapolation) to 100%. Divide miles by the %. Just look at both your actual % and miles, regardless of whether the actual % has shifted vs. what the charge limit was set to.
AlanSubie4Life
Efficiency Obsessed Member
Get your rated miles. (The number next to the battery symbol.)
Switch Display Mode to Energy display (rather than distance). Record your %.
Miles @100% = Miles/%
Note you should do this at a relatively high %. Don’t bother even paying much attention to any numbers below 80%.
Ok. So then the miles and % on the cars display when I enter the car, not what it says on the app when charging is finished?
AlanSubie4Life
Efficiency Obsessed Member
Well...you can charge to a relatively high % and then use the Tesla app’s “extrapolation” feature (change the charge slider and see what it says the range would be at 100%). That should be equivalent. Again, it’s best to extrapolate from a high %, because there is error when extrapolating (more error the lower the SOC).
Benefit of this way is there is no calculating needed. Just use the number. And realize it is an estimate only.
To piggyback off this. Since you can’t tell where in the percentage point you are by just looking at the stated %. I set a destination and look at the energy graph to see if it’s just under 90% line, exactly 90%, or just over 90%. If it’s not exactly 90%, I’ll wait to take my readings until it’s exactly in the middle of a percentage point. I think it helps decrease the variability when extrapolating numbers.
JCtx
Member
May I ask how you do that? From the steering wheel, or on which screen menu? The energy display is the EV equivalent to MPG, correct? I noticed the better route planner asks for that number. Need to find out how to send maps from them to the car, but will try to search for that.
AlanSubie4Life
Efficiency Obsessed Member
It is just on the Car -> Display options list.
Sort of the equivalent of MPG but the reciprocal; it has units of energy per mile rather than miles per unit of energy.
You can get your MPGe (e = equivalent, kind of a silly construct (useless for evaluating costs, but ok for evaluating energy use)) by taking 33700 (Wh per gallon of gasoline) and dividing by the value of Wh/mi.
bigblackshaq
Member
Like many others, I have been concerned with loss of 100% indicated battery range on one of my Model 3s. My P3D (build date 9/13/2018, delivery date 10/8/2018) had gotten down to 270.3 miles at 100% charge on January 20, 2020, at about 30,700 miles, which is a loss of 40.8 miles since the car was new.
I posted about going to the service center to talk with them about battery degradation, which I did on March 9, 2020. It was a great service appointment and the techs at the Houston Westchase service center paid attention to my concerns and promised to follow up with a call from the lead virtual tech team technician. I detailed this service visit in the following post:
Reduced Range - Tesla Issued a Service Bulletin for possible fix
While that service visit was great, the real meat of addressing the problem came when I spoke to the virtual tech team lead. He told me some great things about the Model 3 battery and BMS. With the knowledge of what he told me, I formulated a plan to address it myself.
So here is the deal on the Model 3 battery and why many of us might be seeing this capacity degradation.
The BMS system is not only responsible for charging and monitoring of the battery, but computing the estimated range. The way it does this is to correlate the battery's terminal voltage (and the terminal voltage of each group of parallel cells) to the capacity. The BMS tries to constantly refine and calibrate that relationship between terminal voltage and capacity to display the remaining miles.
For the BMS to execute a calibration computation, it needs data. The primary data it needs to to this is what is called the Open Circuit Voltage (OCV) of the battery and each parallel group of cells. The BMS takes these OCV readings whenever it can, and when it has enough of them, it runs a calibration computation. This lets the BMS now estimate capacity vs the battery voltage. If the BMS goes for a long time without running calibration computations, then the BMS's estimate of the battery's capacity can drift away from the battery's actual capacity. The BMS is conservative in its estimates so that people will not run out of battery before the indicator reads 0 miles, so the drift is almost always in the direction of estimated capacity < actual capacity.
So, when does the BMS take OCV readings? To take a set of OCV readings, the main HV contactor must be open, and the voltages inside the pack for every group of parallel cells must stabilize. How long does that take? Well, interestingly enough, the Model 3 takes a lot longer for the voltages to stabilize than the Model S or X. The reason is because of the battery construction. All Tesla batteries have a resistor in parallel with every parallel group of cells. The purpose of these resistors is for pack balancing. When charging to 100%, these resistors allow the low cells in the parallel group to charge more than the high cells in the group, bringing all the cells closer together in terms of their state of charge. However, the drawback to these resistors is that they are the primary cause of vampire drain.
Because Tesla wanted the Model 3 battery to be the most efficient it could be, Tesla decided to decrease the vampire drain as much as possible. One step they took to accomplish this was to increase the value of all of these resistors so that the vampire drain is minimized. The resistors in the Model 3 packs are apparently around 10x the value of the ones in the Model S/X packs. So what does this do to the BMS? Well, it makes the BMS wait a lot longer to take OCV readings, because the voltages take 10x longer to stabilize. Apparently, the voltages can stabilize enough to take OCV readings in the S/X packs within 15-20 minutes, but the Model 3 can take 3+ hours.
This means that the S/X BMS can run the calibration computations a lot easier and lot more often than the Model 3. 15-20 minutes with the contactor open is enough to get a set of OCV readings. This can happen while you're out shopping or at work, allowing the BMS to get OCV readings while the battery is at various states of charge, both high and low. This is great data for the BMS, and lets it run a good calibration fairly often.
On the Model 3, this doesn't happen. With frequent small trips, no OCV readings ever get taken because the voltage doesn't stabilize before you drive the car again. Also, many of us continuously run Sentry mode whenever we're not at home, and Sentry mode keeps the contactor engaged, thus no OCV readings can be taken no matter how long you wait. For many Model 3's, the only time OCV readings get taken is at home after a battery charge is completed, as that is the only time the car gets to open the contactor and sleep. Finally, 3 hours later, OCV readings get taken.
But that means that the OCV readings are ALWAYS at your battery charge level. If you always charge to 80%, then the only data the BMS is repeatedly collecting is 80% OCV readings. This isn't enough data to make the calibration computation accurate. So even though the readings are getting taken, and the calibration computation is being periodically run, the accuracy of the BMS never improves, and the estimated capacity vs. actual capacity continues to drift apart.
So, knowing all of this, here's what I did:
1. I made it a habit to make sure that the BMS got to take OCV readings whenever possible. I turned off Sentry mode at work so that OCV readings could be taken there. I made sure that TeslaFi was set to allow the car to sleep, because if it isn't asleep, OCV readings can't get taken.
2. I quit charging every day. Round-trip to work and back for me is about 20% of the battery's capacity, and I used to normally charge to 90%. I changed my standard charge to 80%, and then I began charging the car at night only every 3 days. So day 1 gets OCV readings at 80% (after the charge is complete), day 2 at about 60% (after 1 work trip), and day 3 at about 40% (2 work trips). I arrive back home from work with about 20% charge on that last day, and if the next day isn't Saturday, then I charge. If the next day is Saturday (I normally don't go anywhere far on Saturday), then I delay the charge for a 4th day, allowing the BMS to get OCV readings at 20%. So now my BMS is getting data from various states of charge throughout the range of the battery.
3. I periodically (once a month or so) charge to 95%, then let the car sleep for 6 hours, getting OCV readings at 95%. Don't do this at 100%, as it's not good for the battery to sit with 100% charge.
4. If I'm going to take a long drive i.e. road trip, then I charge to 100% to balance the battery, then drive. I also try to time it so that I get back home with around 10% charge, and if I can do that, then I don't charge at that time. Instead, let the car sleep 6 hours so it gets OCV readings at 10%.
These steps allowed the BMS to get many OCV readings that span the entire state of charge of the battery. This gets it good data to run an accurate calibration computation.
So what's the results?
On 1/20/2020 at 30,700 miles, I was down to 270 miles full range, which is 40.8 miles lost (15.1 %). The first good, accurate recalibration occurred 4/16/2020 at 35,600 miles and brought the full range up to 286 miles. Then another one occurred on 8/23/2020 at 41,400 miles and brought the range up to 290 miles, now only a 20 mile loss (6.9 %).
Note that to get just two accurate calibration computations by the BMS took 7 months and 11,000 miles.
So, to summarize:
1. This issue is primarily an indication/estimation problem, not real battery capacity loss.
2. Constant Sentry mode use contributes to this problem, because the car never sleeps, so no OCV readings get taken.
3. Long voltage stabilization times in the Model 3 prevent OCV readings from getting taken frequently, contributing to BMS estimation drift.
4. Constantly charging every day means that those OCV readings that do get taken are always at the same charge level, which makes the BMS calibration inaccurate.
5. Multiple accurate calibration cycles may need to happen before the BMS accuracy improves.
6. It takes a long time (a lot of OCV readings) to cause the BMS to run a calibration computation, and therefore the procedure can take months.
I would love if someone else can perform this procedure and confirm that it works for you, especially if your Model 3 is one that has a lot of apparent degradation. It will take months, but I think we can prove that this procedure will work.
Candleflame
Active Member
Noone really knows and even generally agreed on battery care sometimes leads to more degradation than expected.
Common things are:
- try to not deep cycle the battery
- do not charge to high or discharge too low
- let the car rest at i.e. 75-80% rather than 90% in hot climate
- dont supercharge (often)
However on one of the old surveys it seemed that cars which just do a daily charge to 92% (used to be the daycharge limit) actually had the least rated range degradation.
There are also plenty of frequent supercharging vehicles with exellent mile retention. The only thing we know IS bad for the battery (Tesla Service sent this as the reason why a fleet cars HV battery failed) is to supercharge frequently from 0 to 100% without letting the battery rest for an hour or so - likely as the system can potentially overshoot as the BMS isnt sure how full the battery is. Given that the BMS tends to underread range and post AC destination charging I have seen a range increase of up to 4% when resting the battery I presume that it is hence possible to superge to i.e. 105% by accident which causes a lot of degradation.
There are also plenty of salvage Model S/3s in the united states which sat with the 12V battery failing and the high voltage battery sitting at 0% for months which dont have any worse than normal degradation. Given that a lot of lithium ion manufacturers recommend storing the battery discharged to 0-1% and then freezing them it is likely that deep discharges do not matter at all, nevermind that 0% on a Tesla is actually around 6-7% (4.5% buffer plus maybe 2% brick protection). As long as the car is not floored at least.
We also know that there seem to be a lot of Model 3s which get cycled heavily from 60% - 5% all the time and basically hop from supercharger to supercharger and they have very little to no degradation which suggests that it is actually not harmful at all for the battery to get discharged or to supercharge as long as this is done at the lower end of SOC. Indeed from studies from the battery university it seems that cycling from i.e. 60 - 10% seems to be slightly more healthy than cycling from 80% - 30%.
Another thing we know for sure is that the initial batch of Model 3s going to Australia seem to have a lot more degradation than other cars (mine included) - they all had 12V battery failures so presumably the HV battery sat at <5% for prolonged periods which kind of puts a hole in my low SOC theory above. I have also noted that the degradation of those vehicles seems to be similar regardless of how owners drive their cars. I.e. I do a lot of slow DC charging and frequent deep cycling as well as discharge the battey often to <5% yet I seem to have the same degradation as someone who just does a lot of city driving and AC charging.
So the answer is that we just dont know and its probably wisest to charge to 90% (or maybe 80-85% in hot climates) and just forget about it.
Thanks, lots to think about but I like your final comment, “just forget about it” and I’ll add enjoy the car.
JCtx
Member
May I ask what does 'deep cycling' the battery mean??? Got delivery of the 2021 LR on the 29th, so free supercharging for a year, and free FSD for 3 months. My current plan based on this thread is to charge to 90% in fall/winter/spring, and 80% in summer (hot TX here), and recharge at 20% as a minimum (20 to 30%)... or once a week at least, even if a little higher than 30%. This is without traveling, of course. And from a 32A 15-40 220V outlet I'll get installed next week. Does that sound good? Or if we're not using the car, should we leave it until it's around 20, even if it takes longer than a week? Thx.
NOTE: My car just has a line to limit charging percentage, and it doesn't even say what it is, but seems like each line is 10%. And I cannot set it between lines, so not possible to charge at 85% in my car; I tried. So left it at 90%. Is that normal? I'd like to see what percentage is limited to, if possible.
NOTE: My car just has a line to limit charging percentage, and it doesn't even say what it is, but seems like each line is 10%. And I cannot set it between lines, so not possible to charge at 85% in my car; I tried. So left it at 90%. Is that normal? I'd like to see what percentage is limited to, if possible.
Candleflame
Active Member
Charging to only 80% or maybe 85% makes sense in texas summer but the benefit of it isn't currently clear. It may be very limited as when the car displays 90% you are actually only charged to around 85% to start with (Teslas only charge to 4.15V, whereas nominal agreed 100% charge for lithium ion cells is 4.2V. So a 100% charge on a Model 3 is around 94% true SOC). if you charge to 80% (75% true SOC) or 90% (85% true SOC), the reactivity with heat is going to be low either way and probably doesnt make much of a difference. I guess a nice middle ground would be to charge to 85%.
Deep cycling the battery means if you i.e. charge to 90% but rather than plugging it in every time you come home at 70% is to just let it drop until its i.e. 10% you then plug it in. Or you go on a lot of roadtrips and do a lot of discharges from i.e. 100% to 2% before you charge it back up to 90% or whatever. We know that deep cycling is harmful to the battery, but as I said above, Teslas only charge to 94% SOC And 0% on a Model 3 corresponds to maybe around 6% true SOC. We know that th effect of deep cycling is greatly diminished below a 90% cycle (so discharging a battery from 100% -> 0% is one cycle, discharging a battery from 100% to 50% twice is also one cycle) so again the benefit of doing this is uncertain. I can certainly tell you that I would never deep cycle a battery on purpose or just for the hell of it as this IS harmful. We just dont know how much. Just plug it in and charge to 80% or 85% or whatever when you get home.
I might add here that originally Teslas only had 2 settings for charging - day charge (92%) and trip charge (100%). Tesla also advised everyone to always keep the car plugged in so most old Model S spent a lot of time sitting at 92%. There were some smart people who interupted the charge to theyd only charge to i.e. 80% daily rather than 92% as they felt this was better for the battery. Interestingly enough on a survey here a few years ago the people with the lowest degradation just plugged in everyday and let it charge to 92%. Noone quite knows why and there are different theories re: miscalibration vs true degradation.
Some people deep discharge the battery w/o deep cycling. I.e. in Australia we have a bad charger network so a lot of people - me included, often arrive with <5% and may only charge up to 50% before discharging back down to <5%. Operating the car at low SOC has been a source of debate on tesla forums as keyboard warriors generally proclaim that being on the low end of SOC is harmful to the battery.
Research has shown that that does not really seem to be true - in fact it is seems to be beneficial for the battery to be cycled on the low end of SOC rather than have cycles at the high end of SOC. I presume Tesla advises against this practice as driving the car "hard" at low SOC puts more strain on the battery due to high discharge current. Either way, deep discharging the battery means that if you travel to a supercharger you get significantly higher speeds which is why some people do like to cycle their battery on the lower end of normal when on road trips.
If you arent using the car for a few weeks I'd charge to 50-60% and just leave it plugged it.
The big lines in the app mean 10% but you can set it individually down to a single %. If you cant do it on the Model 3 screen then you just have fat fingers or something...
32A 220V is plenty to charge at home.
@Candleflame, your reply had a lot of good information, but this part is not correct. With the exception of the 10% top locked SR and recent shenanigans with the new packs in EU cars, Model 3 batteries charge up to 4.2V per cell. This has been widely seen and reported.
Here’s an example at 100% SOC showing 403V at the pack and 4.20V at the cell level. Start at about 2:40.
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dhrivnak
Active Member
One change is to remember the ABC’s of EV’s. Always Be Charging. Plug in every day not once a week waiting to reach 20-30%.
Yep. 4.2V at 100% is normal in most Teslas.
At 80%, I recorded cell voltages of ~4.05V (I recently got a harness and the "scan my tesla" app). I haven't fully mapped out all various voltages at states of charge, but assuming that 90% is around 4.1V, both are a bit higher than what I would recommend if letting the car sit a while. For maximum cycle life most recommend a maximum charge voltage of around 4.0V, this is probably 70-75% SOC. I would then opt to recharge between 25-40% (for maximum cycle life).
The problem, as highlighted in this thread, is that this may not be suitable to keep the pack balanced well and give the BMS enough information to accurately gauge the pack's true capacity. In my car, I was following the 70%-30% charge cycles and displayed range dropped a bit, but remained around 310 miles (Model 3 LR RWD). But after COVID hit and I stopped driving much, I switched to 50%-30% and that really caused a drop off in indicated range (down as low as 285 miles). I have since started charging to 70-80% (still recharging around 30%) and some of those miles have come back. I probably need to charge to 90% a few times to get back over 300 miles displayed range. I'm just waiting for a longer trip so I don't leave the car sitting for weeks. Cell imbalance is around 6 mV right now, which is higher than I'd expect from looking at other people's data, so I suspect that is causing most of the indicated range drop.
Anyway, I'm not worried about the indicated range drop. All the science indicates that it's just paper losses and that keeping the SOC between 30-50% is best for retaining actual capacity of the pack. Then if needed can go to 90%-30% cycles and get that indicated range back.
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