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LFP. Weekly Charging vs Daily Charging
- Thread starter arnyswart
- Start date
Tam
Well-Known Member
First you need to confirm if yours is LFP. The manual tells you how to ID it.
Go to your charging screen where you can slide from 50 to 100%. If it has notation of "Daily" and "Trip" then it is not LFP and you should not charge 100% unless on a road trip.
If you have LFP then you should listen to the manual and charge to 100%. Some refuse to follow the 100% settings and got into trouble.
Punchbuggy
Member
But the MY is coming from China and therefore will be LFP? If that's still the case, isn't the key matter how often you need to charge it to 100% (which I recall someone proposing weekly)? The LFP benefits from that, whereas it's not wise for NCA battery cars.
Tam
Well-Known Member
I don't know. That's why you need to follow your manual instructions to find out.
In general, LFP is heavier and takes more space so it's fine for lower-trim that has less range and less performance.
On the other than, NCA is lighter and offers more performance so it is preferred in higher trim.
So which trim did you get? Cheaper or more expensive one? Longer range or lesser range. Fast acceleration or slower acceleration?
LFP- You are fine to keep it charged up to 100% all the time. If you cannot then you need to get it to at 100% at least weekly for the BMS to stay as accurate as possible.
There should be no difference in battery life if you charge smaller amounts more frequently versus larger amounts less frequently. Batteries have a Cycle Life rating and one cycle means charging from 0 to 100% and discharging back to zero again. This is the equivalent of discharging and recharging the battery by 50% twice.
To increase the longevity of your battery keep it state of charge away from extremes, in particular don’t let it go too low and if you are forced to let it get close to zero, plug it in as soon as possible. Model 3 and Y now come with different chemistry batteries depending upon the version you buy and some allow you to charge to 100% others recommend no higher than 90% unless you need it for a long trip and will be leaving soon after the charging is completed. Teslas that have this requirement will have a “daily“ and “Trip” section in the charge selector.
Battery management on a Tesla is way more advanced than your average PHEV as can be attested by my 7.5 year old Model S that has lost only about 10% of its original range.
Or just look at your VIN. The 7th character tells you what kind of battery it is.
If it’s F, it’s LFP. Go to 100% as often as possible, at least weekly, preferably daily.
If it’s E (or the less common H, S and V), it’s a more conventional battery. Avoid 100% unless you’re about to set off on a long drive.
LFP batteries are tolerant of different charging styles. Even if frequently charged to 100%, they may still last for a million miles. So you can pretty much charge them however you like.
If you want your car to last for a very long time, longer than, say, 10 years, and you want to treat the battery better, charge it to 70% whenever you can charge, like every day. 70% is a sweet spot for LFP batteries, because calendar ageing ist just as high as at 40%, but lower than at higher states of charge, like 80%, 90%, or 100%. Those show somewhat increased rates of calendar degradation.
Charge it to 100% whenever you foresee an advantage, like just before a long trip. Tesla once recommended charging to 100% once a week, not because that's good for the battery chemistry, but simply because this calibrates the battery managemen system (BMS) and balances the battery modules.
I guess, when you do not charge to 100% for a longer time, the BMS might show slowly reducing values of the whole battery capacity. So as long as it shows sufficient range for your needs, I don't see any good reason to keep charging to 100% weekly. But this is not fully researched, so it may still be a good idea to follow Tesla's recommendation.
Calendar degradation is significantly lower at low states of charge (SoC), like 30%, 20%, 10%, and almost nonexistent at 0%. But it is impractical to have a car standing there that you can drive only for a few miles before having to recharge. So that's probably not a good idea. Also, the closer you get to 0%, the higher the risk of inadvertent deep-discharge, which would destroy the battery if it gets below the zero point. You'd also run the risk of the 12 V battery not getting charged and possibly running empty, leading to a seemingly dead car.
The other factor determining the rate of calendar ageing is temperature. One could argue that keeping the battery at a lower SoC is much more effective on hot summer days, while you could consider keeping the battery at a higher SoC in winter, because of the slower degradation at low temperatures. This plays into the hands of avid winter drivers, because you usually need a higher SoC in winter for heating.
But let me repeat, if you don't see any need to prolong the battery's lifetime, it is quite OK to ignore all of this and charge as much as you like.
If you want your car to last for a very long time, longer than, say, 10 years, and you want to treat the battery better, charge it to 70% whenever you can charge, like every day. 70% is a sweet spot for LFP batteries, because calendar ageing ist just as high as at 40%, but lower than at higher states of charge, like 80%, 90%, or 100%. Those show somewhat increased rates of calendar degradation.
Charge it to 100% whenever you foresee an advantage, like just before a long trip. Tesla once recommended charging to 100% once a week, not because that's good for the battery chemistry, but simply because this calibrates the battery managemen system (BMS) and balances the battery modules.
I guess, when you do not charge to 100% for a longer time, the BMS might show slowly reducing values of the whole battery capacity. So as long as it shows sufficient range for your needs, I don't see any good reason to keep charging to 100% weekly. But this is not fully researched, so it may still be a good idea to follow Tesla's recommendation.
Calendar degradation is significantly lower at low states of charge (SoC), like 30%, 20%, 10%, and almost nonexistent at 0%. But it is impractical to have a car standing there that you can drive only for a few miles before having to recharge. So that's probably not a good idea. Also, the closer you get to 0%, the higher the risk of inadvertent deep-discharge, which would destroy the battery if it gets below the zero point. You'd also run the risk of the 12 V battery not getting charged and possibly running empty, leading to a seemingly dead car.
The other factor determining the rate of calendar ageing is temperature. One could argue that keeping the battery at a lower SoC is much more effective on hot summer days, while you could consider keeping the battery at a higher SoC in winter, because of the slower degradation at low temperatures. This plays into the hands of avid winter drivers, because you usually need a higher SoC in winter for heating.
But let me repeat, if you don't see any need to prolong the battery's lifetime, it is quite OK to ignore all of this and charge as much as you like.
BMS calibration comes from a range of stable readings across different states of charge, not from charging to 100%. Think of calibration as trying to draw a straight line on a graph through a number of data points, its much easier if they're spread across the full range.
Cell balancing needs charging to 100% and leaving it plugged in.
I've heard that before, but I have doubts. However, the topic is so complex that we'd need a lengthy discussion, and arguing might still not lead to a convincing conclusion. On top of this the question is not that important for practical purposes. Since Tesla recommends charging to 100% from time to time, I think we already know enough to treat our cars well.
If you had a link to an authoritative source though, I'd be grateful.
Appreciate not wanting a lengthy discussion
My thoughts are based on
How I Recovered Half of my Battery's Lost Capacity
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...
teslamotorsclub.com
And
Tesla battery management system (BMS) calibration
Tesla battery management system (BMS) calibration instructions
tesla-info.com
If you Google the topic on here you’ll also find more people saying they’ve done essentially these things and got back range.
I guess the only other thing I’d add is it kind of makes sense to me that a range of voltage readings across the spectrum might help but I don’t know why really. The energy used between the different voltages might also be useful.
At the risk of having that lengthy debate what makes you doubt it?
I suspect the first of the two links refers to NMC batteries, not LFP. LFP batteries have a near-constant voltage at a constant load or at no load over a wide range of states of charge. A more precise determination of the SoC from the voltage is only possible at very high and very low SoC levels. Therefore the recommendation to leave the battery without load at various SoC levels makes little sense for LFP batteries. Intermediate states of charge are determined by some kind of dead reckoning and recalibrated only very high and occasionally at very low states of charge.
The description of the balancing resistors makes no sense to me. I guess that the precise description of how balancing works got lost somewhere along the way. But balancing is only a secondary concern and not overly relevant to the topic, so I've never gone into that. It seems to work well enough for the most part.
Also, the first link asks the Tesla driver to do an enormous amount of babysitting, so much that I would rather return my Tesla than having to go through such excessive, time-consuming procedures that temporarily impede the usefulness of the car. Fortunately, I believe, such babysitting is not needed. The BMS might show some phantom degradation, but the deviation will stay within sensible limits. Ultimately it will readjust sufficiently well with normal use.
The second link leads to a recommendation officially from Tesla (rather than the private opinion from some Tesla employee), so I deem it more likely to be correct. Sensibly it mentions that very low and very high states of charge are useful for calibration, which would be especially true for LFP batteries.
By the way, it also mentions something I have long presumed, namely that the BMS is conservative in its intermediate estimates, such that it prefers a pessimistic estimate of the remaining charge over risking that the car stops while still showing a positive SoC. That's how I would program it, since I don't see any other good way.
So what's the conclusion? There is no need to babysit the battery, except that you should charge it to 100% before a long-distance drive.
I'm not sure where the recommendation to charge fully once a week comes from. Perhaps Tesla isn't quite sure about the BMS always showing sufficiently pessimistic SoC values. I don't do that and have not had any problem so far. If the values ever were too optimistic (too high), rather than pessimistic, I would expect to observe the SoC racing down when the battery voltage begins to shrink, i.e. somewhere between 20% and 10%. That would still leave me 20 or 30 true miles to find a charger, but I want to experience that before I believe it. My best guess is that I will never see it.
The description of the balancing resistors makes no sense to me. I guess that the precise description of how balancing works got lost somewhere along the way. But balancing is only a secondary concern and not overly relevant to the topic, so I've never gone into that. It seems to work well enough for the most part.
Also, the first link asks the Tesla driver to do an enormous amount of babysitting, so much that I would rather return my Tesla than having to go through such excessive, time-consuming procedures that temporarily impede the usefulness of the car. Fortunately, I believe, such babysitting is not needed. The BMS might show some phantom degradation, but the deviation will stay within sensible limits. Ultimately it will readjust sufficiently well with normal use.
The second link leads to a recommendation officially from Tesla (rather than the private opinion from some Tesla employee), so I deem it more likely to be correct. Sensibly it mentions that very low and very high states of charge are useful for calibration, which would be especially true for LFP batteries.
By the way, it also mentions something I have long presumed, namely that the BMS is conservative in its intermediate estimates, such that it prefers a pessimistic estimate of the remaining charge over risking that the car stops while still showing a positive SoC. That's how I would program it, since I don't see any other good way.
So what's the conclusion? There is no need to babysit the battery, except that you should charge it to 100% before a long-distance drive.
I'm not sure where the recommendation to charge fully once a week comes from. Perhaps Tesla isn't quite sure about the BMS always showing sufficiently pessimistic SoC values. I don't do that and have not had any problem so far. If the values ever were too optimistic (too high), rather than pessimistic, I would expect to observe the SoC racing down when the battery voltage begins to shrink, i.e. somewhere between 20% and 10%. That would still leave me 20 or 30 true miles to find a charger, but I want to experience that before I believe it. My best guess is that I will never see it.
I found this great YouTube video which explains the different chemical makeup between NCA and LFP. Sheds some light on why LFP can and should be charged to 100% with little to no degradation.
LFP Battery
LFP Battery
My hunch is that it's the opposite - Tesla knows the BMS is being slightly pessimistic (for good reason, as you mention earlier), but that pessimism is essentially a systematic error term that will accumulate over many partial charge/discharge cycles, to the point that it shows an excessively low range estimate. Charging the LFP battery to 100% regularly will reset that accumulated error term in the estimate.
More than charging to 100% and seeing Charge Complete, leave it plugged in until it draws no current. This is when the cells balance and you may see the estimate range when full correct (upwards). If you want to nerd out, get Scan My Tesla app and watch what happens to individual cell voltages.
