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Model 3 Performance Battery Degradation One Month (Story)
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TimothyHW3
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This might not be due to the charging habits, but it very well might be.
I hear that from US drivers that supposedly "Tesla" advices drivers to keep the battery at 90%.
This couldn't be further from the truth. "Tesla" says that you CAN charge to 90%, but in no way will charging to 90% daily be beneficial to the battery nor BMS.
Same goes for the video you posted. Charging to 90% ok, but not daily from 70%-90%
It hurts the battery because it keeps the Voltage very high and it hurts the BMS, because the BMS doesn't really know where the bottom is.
To me it sounds like the problem is with your charging. Go and ask Tesla to reset your battery again and this time charge from 25/30%-80-85%.
Meaning you charge to 80% and start driving and only charge it again when you are at 25% or so. Def. avoid charging above 50-60%.
Try to avoid any phantom drain by disabling sentry, car alarm, dashcam (pull the stick).
Keep it like that for 2-3 weeks and then do a 10%-100% charge.
I hear that from US drivers that supposedly "Tesla" advices drivers to keep the battery at 90%.
This couldn't be further from the truth. "Tesla" says that you CAN charge to 90%, but in no way will charging to 90% daily be beneficial to the battery nor BMS.
Same goes for the video you posted. Charging to 90% ok, but not daily from 70%-90%
It hurts the battery because it keeps the Voltage very high and it hurts the BMS, because the BMS doesn't really know where the bottom is.
To me it sounds like the problem is with your charging. Go and ask Tesla to reset your battery again and this time charge from 25/30%-80-85%.
Meaning you charge to 80% and start driving and only charge it again when you are at 25% or so. Def. avoid charging above 50-60%.
Try to avoid any phantom drain by disabling sentry, car alarm, dashcam (pull the stick).
Keep it like that for 2-3 weeks and then do a 10%-100% charge.
Wait...so are you saying Tesla's charging guidelines are wrong on this? The manual specifically says to charge nightly and to keep it plugged when not in use, if possible. This is what has always been the required standard are you saying not to do that?
What was your rated range at full charge at the time of this measurement?
In your latest Teslafi report I see 272 miles. However 251.61/0.88 = 285.9 miles.
If we use battery % then the accuracy of this test becomes +-0.5% however if we know the rated range, that brings it down to +-0.2% (plus the accuracy of the average consumption)
198.44*308 = 61.12kWh
61.12/0.88 = 69.45kWh
now let's add min max to check rounding errors. 308Wh/mile could be 307.5 - 308.5
and SoC % could be 88 to 88.99 (for some reason SoC is not rounded but truncated)
198.44*307.5/0.89 = 68.6kWh
198.44*308.5/0.88 = 69.6kWh
So your battery's capacity is somewhere between 68.6 and 69.6kWh. If you have the rated range at the time of the measurement, then this calculation could be more accurate.
The usable capacity of a brand new battery is 74.5kWh. So yours has around 6 - 7% degradation assuming the measurement and the BMS data was ok. A little on the high side. That is very similar to what Tesla Bjorn has on his Model 3P (69.8kWh). Most people are at around 4-5% degradation at this mileage.
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Speculation is that guideline is to simplify for mainstream EV users so that there's no range anxiety, among other things to prevent consumers driving on low charge.
I used to time it where I'm close to 20% SOC or lower and go supercharged my car up to 80% when I just got my car, but it's proving very difficult due to having a toddler and an infant. Now, it's 90% max and generally <50% or when I know I need to just charge it back to 90% when >50% because I know I'll be making runs where I just don't want to be low on SOC by the time I'm home.
I have supercharged up to 70% at times, but don't know how much of that tricked the BMS, as I adjusted to 80% and then 90%.
If everything is correct in the BMS then it should not. Actually there is a bottom buffer. One can drive an additional 10-15 miles before it stalls. But if the BMS is incorrect for whatever reason (imbalanced cells or stg) then it may stall before that. For some older cars it stalled at 15%.
New batteries have 78kWh nominal capacity. Minus 3.5kWh buffer. = 74.5kWh usable capacity.
Later on with some degradation the buffer gets reduced as well. Bjorn has 73.5kWh nominal capacity minus 3.3kWh buffer. He measured 69.8kWh in his capacity test.
TimothyHW3
Active Member
I think I explained a lot of things in my post. If you wish you can try what I suggested. If not, then oh well.
Tesla follows the ABC(Always Be Charging) rules in manual because if they start linking graphs and charts they will only confuse people.
Most folks don't make the difference between a kW and kWh...Tesla doesn't make a great deal explaining things, especially the energy bar amd graph and charging(curves, speed, %). Probably due to incompetent and underpaid staff or/and lack of interest.
If you were just topping up the 70-90% the whole time and after a reset the battery reports higher miles, meaning there is more capacity available in kWh - this is your problem most certainly.
diamond.g
Active Member
I actually wondered if they changed the buffer, when I first got this car the buffer read at 3.5 kWh, now it reads 3.3. It would be nice if someone with a new car could get the numbers from the pack before putting too many miles on it to verify if they are reducing the buffer as the pack ages.
Alright, you’ve convinced me. I’ll do 30-80% charges for a few weeks and see how it goes. Thanks.
just one question: why isn’t this phenomenon apparent in my 2017 Model X? Charging habits are identical, and I’ve seen zero reduction in rated range in the 7 months I’ve owned it...
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TimothyHW3
Active Member
30-80% will help only AFTER the CAC reset. Push Tesla to do it and do the 30-80% for a month and see how that goes. If you go 30-80% now it will not do anything, afaik. Also, try to top it up to 100% after a month or two and start right away and drive it down to 10% and charge it back to 80-90. Plan a vacation trip or something
As for X/S, not sure, bigger battery, different chemistry and BMS who knows.
TimothyHW3
Active Member
It is 3.5kWh when new and then it gradually falls down to match the degradation. Mine reads 3.4kWh on 10,000miles and 75.9kWh or about 1.5% degradation. I have seen it go as low as 3.3 on more mileage cars, so you are there now.
Edit: Correction. I have a record of one Model 3 P with 3.1kWh that has only done 10,000 miles and had a 10% drop in the first couple of thousand miles or so and the nominal reports 70kWh. He has a very high cell imbalance and has charged to 90% daily and never dropped below 40% or so. Pretty much what the driver above has been doing. So I think it is just uncalibrated BMS like in @gaspi101's case
So what happens to the buffer - as far as I can see, there is hard coded algorithm. If the BMS "thinks" you are at 75kWh, then the buffer is 3.4kWh. If the BMS is at 74kWh nominal, 3.3 and so forth. I am sure someone can reverse engineer the math and at which points the drop happens. But from what I am seeing it is either hard coded or some math algorithm.
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30-80% will help only AFTER the CAC reset. Push Tesla to do it and do the 30-80% for a month and see how that goes. If you go 30-80% now it will not do anything, afaik. Also, try to top it up to 100% after a month or two and start right away and drive it down to 10% and charge it back to 80-90. Plan a vacation trip or something
As for X/S, not sure, bigger battery, different chemistry and BMS who knows.
Ah, ok. Well, in that case, let me just say that my rated range was within acceptable parameters for more than SIX WEEKS after the CAC reset. The sudden losses occurred afterwards. Here's a current report and I've added the dates of the recent dramatic drops--CAC reset was on 7/16/19: Imgur
I'll also add that on 10/6/19 (where the rated range drops from 284 to 275 in one charge) was during a roadtrip, where I charged up to 100% before leaving, and then discharging to around 20%, and then supercharged with discharges between 20% and 90% several times--therefore, the battery was getting a good idea of the top and bottom ends of its capacity...To my mind, and based on your info, this is degradation or bad cells, not a charging habit issue....What do you think?
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TimothyHW3
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I am not an expert, but I have the feeling it is BMS and not the battery. The reason being is that after a reset it calculated properly.
This is like having a bad gauge in the tank - you have 60 but it reports 40. When you change it - it shows 60 again. If you really had only 40, it would've shown 40, since the gauge is new, and not 60, which you wouldn't have.
Same with the BMS - they reset something and the BMS started calculating the total capacity from the top kWh it measured. This proofs also why you had no issues during the 6 weeks. I think you tripped it during charging or something or a sensor in your battery is not correct. I'd say keep poking at them and have it escalated to a tech guy in Fremont. I am sure Tesla will be interested to know what causes this.
Without access to the BMS nobody can tell you waht is going on, except some Tesla tech. But like I said, my gut feeling is bad charging habbit and/or a combination with some BMS sensoring going wrong.
TimothyHW3
Active Member
Make sure to tag me and make a new big post on the forum to report what happened. This will be important to everybody. Ask Tesla what they are doing and what the advice for charging is in the future and what triggers this sudden drop. And if it is the battery, what are they "fixing" if anything.
Basically any information you can get. 15% drop is not normal.
If I get anything that useful and accurate from Tesla , I would be surprised, to be honest. But I promise to keep you posted. To tell you the truth, now, that I'm at the 15% mark, I'm kind of hoping the degradation to quickly drop 15% more so I can demand a warranty repair. LOL
284.86*242.87 = 69.18kWh +-0.2%
Please share one more trip with this lower rated range when you get a chance. I wonder what's changing so wildly.
TimothyHW3
Active Member
I have the car now at 3.89V at 57% sorry I missed the 3.92V, but my guestimate it is around 60%-65%.
But charging to 60% only might trip the BMS, if you don't let it go much up and down now and again.
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