How I Recovered Half of my Battery's Lost Capacity

[AZAV8R]

Thank you, TEG! I can see that there are some system-limitations for newbies. Does that include not having a "like button" yet? Or am I missing it somewhere? How long will I be in the newbie status?

[ Mod edit: Forum features will start to appear as your post count increases. ]

 

[AlanSubie4Life]

I still don't understand the letting batteries at low SoC "rest." I get that they will be warm due to high amps but the car should be able to just cool them off right? Seems like it would be best to get it back up to 25%+ as soon as possible. What am i missing?

Yeah, not sure why a lot of resting and cooling would really be needed for the typical 15-25kW draw (~240Wh/mi at 60mph or ~320Wh/mi at 75mph).

It just is not that much draw. Barely higher than a standard AC charging wattage. Obviously in reverse, but not sure about the “resting after using” bit of lore. Might be different if you’ve been tracking the car. But regular driving is just sipping at that battery.

I was driving through Central Valley at 80mph recently in mid-90s temps. And just one time did it activate preconditioning for Supercharging - and based on the noises (no whining from the motor like in winter - just pumps running) and the message, it appeared to be COOLING activated (not warming like in cooler conditions). So it seems like the car will try to deal with high or non-optimal battery temps anyway. This happened only when I temporarily
(accidentally) navigated to a very close supercharger. I wonder if for more distant destinations, when cooling is needed, it doesn’t even bother to do anything super special, and instead passively ensures that the correct target temperature is achieved on arrival (via opening louvers, redirecting coolant, etc.)

 

[AZAV8R]

Thank you, TEG! I can see that there are some system-limitations for newbies. Does that include not having a "like button" yet? Or am I missing it somewhere? How long will I be in the newbie status?

[ Mod edit: Forum features will start to appear as your post count increases. ]

 

[camalaio]

Jeez this thread really blew up in a short time!

So. Hi, "that guy" here. Unfortunately I must embrace it, and recognise I'm the party pooper. Sorry.

There's some really really good advice in the OP, surrounded by some really false details, and also a bad suggestion or two. This does not eliminate the fact there are good points though, which I've summarised at the bottom.

I struggled with posting this, as it seems combative and/or argumentative? But that isn't my intent. @SomeJoe7777, this ain't your fault for "getting wrong" so please don't see it that way. Seems like you were fed a bad explanation IMO. This actually happens a lot from Tesla Service employees, unfortunately (as they're pressured into offering some explanation with their current understanding). You brought new information to us, which is very appreciated!

The open circuit voltage is indeed important, this has been known for a while but good to talk about directly (it gets lost in the misguided "balancing" threads every time). The voltage swings quite wildly when driving, but your battery gauge is resilient to these swings while still providing a very accurate report of remaining capacity. This is an admirable component of Tesla's battery meter.

There's much for the BMS to learn during a drive (changes during discharge and regen can reveal a lot), but a non-sagged open-circuit voltage is fairly representative of the battery state especially when battery temperature is also known (and indeed, it is to the car).

---

The bleed resistor thing sounds all wrong. Balancing setups generally aren't like this (maybe never?), for many reasons:

• The bleed resistors, for balancing, cannot (reasonably) be permanently draining
  • By definition, the battery is not open-circuit if there's a reasonable load across any of the cells (e.g. for balancing)
• Being the "primary cause" of vampire drain measured in the wild would require some unrealistic values
  • Stats says ~60W median for LR. 96 series bricks means each brick drains 0.625W
  • Implies chonky 1W resistors. These would be visible on the BMS boards. I see no such resistors. I don't even see 1/4W ones.
  • At 4.0V (reasonable guess of average SoC, ~73%), that implies a ~25 Ohm resistor. That is a very, very low value for a "bleed" resistor.
• If the bleed resistors were 10x higher (and always engaged), voltage would reach steady state faster, not slower. Higher resistance equals less power draw. Less power draw sags the battery voltage less. Less sag means being closer to steady state or "open-circuit".
  • That would also imply 2.5 Ohm "bleed resistors" on S/X. This is more into current shunt territory than bleeds, and would indeed cause massive vampire drain if always engaged. But S/X are not that bad.
• Most importantly, bleeding all bricks simultaneously just wouldn't be an effective way to balance - no balance is actually occurring this way, just a fixed drain no matter what the capacity of that brick is, which would actually induce imbalance over time.

---

I find 3+ hours to stabilise voltages incredibly hard to believe (yet I have no data to support this). What's more believable to me is that this is an upper bound for some common tasks Model 3 is doing before going to sleep:

• Sometimes the car fetches new firmware and/or map data after a drive. It seems to remain fully awake while it downloads. As downloads are large and the car often gets spotty WiFi (garage or outside), these take a while.
• Sometimes the car will upload data after a drive. See above, but note upload speeds are generally much slower on home internet.
• The blower will continue to run for a surprisingly long amount of time if the AC was on, to reduce condensation leading to the moldy smell.
• When the battery is very warm, it seems to stay awake longer (not necessarily using the chiller to cool it off, just running the pumps and going through the radiator).

Now, stabilised could've meant "balanced" I suppose, which kind of makes sense in the post? But this doesn't seem right?

---

Anecdote time. It just so happens that ever since switching to 240V charging (months and months ago), our charging habits would be ideal for this OCV theory. Especially in the pandemic where we leave the car unplugged at various percentages now, it has more of a chance to gather more readings.

The result of that? The reported capacity plummeted nearly all at once, no gain. It also still varies +-1% despite all this seemingly good data it should be getting. And where it ended up seems about right for a healthy battery, reporting about 5% degradation on a car with 40,000km on it.

What I mean to highlight by this is that, if true, it can go both directions. One person may "gain" range, another may "lose" it.

---

I'd put these as the "good takeaways" of the OP.

• Let your car sleep. This has multiple benefits, but accurate measurement is one!
  • Yes, don't run Sentry 24/7. Car wasn't designed to be a dashcam, and does that job poorly.
• Any "calibration" is just that, and hasn't increased the actual capacity of the battery.

And don't do these:

• Don't: Charge to 100% to "balance". This happens at lower percentages anyways as well, and balancing to an uncommon state actually offsets it in a non-ideal way. Balancing would also take a lot of time, so doing this right before a trip doesn't accomplish that anyways.
• Don't: Skip charging to provide more data points. While I've found some vampire drain benefits to being unplugged, not having the capacity when you suddenly find need for it is not good. There is no sense in stranding yourself because you left the car unplugged at 20% just so the battery meter is very very slightly more accurate. That's like 50mi of range of a brand new SR+ in ideal conditions on flat ground.
• Don't: Take TeslaFi/Stats/etc. graphs as accurate. There's so many problems with the way these report capacity in general, and can paint pictures that don't reflect reality.
• Don't: Take Tesla Service's guidance on everything regarding batteries. Some do have some generally good advice, but some have their own wild theories. They are often not battery experts, they are mechanics. That said, don't take some internet dude's advice either, me included!

---

Rapid question answering time! (it seemed like most of these weren't responded to)

Does leaving climate controls on cause the battery not to sleep and any thoughts on what to do when I have to park outside with no shade and a month straight of temps near or over 100 degrees.

I have seen a significant loss in displayed range and I can’t help but feel like it is from my vehicle running the air to keep the computers cool. Any thoughts or input on this?

Yes. The AC and heater are both high-voltage components and will draw from the battery at all times if on.

My suggestion would be to not leave the climate controls on. Turning them on even just 2 minutes before you get in the car does wonders, if possible (I realise connectivity can be an issue in some places).

If you have Cabin Overheat Protection on (it is by default), that could explain some of your drain (but it doesn't run that if it hasn't been driven for more than 12 hours). The computers are actually liquid cooled, and the AC wouldn't need to run for that (just passive heat rejection via the coolant loop and radiator is way more than enough).

I was going to ask this, but really this is just to let the car recalibrate what it thinks it has capacity wise. It has no actual effect on capacity or health of the pack, just how it is reported, is that correct?

Mostly, yes. Small effective capacity gains may happen via balancing, but that's a whole separate topic IMO. If there are gains to be had by balancing, they are small. If you have significantly reduced capacity due to balance issues, you have a physical battery issue that is beyond correctable by balancing.

Great information in this post. Here's how I think it applies to my situation, given this background:

I have a 2019 M3LR AWD (Scarlett) that started its life with my wife and I in July, 2019. When I drove out of the parking lot, its range showed 315. In the year that we have driven it, we have covered just over 7,000 miles. We're seniors, and retired - no jobs or daily driving unless we want to go somewhere. Scarlett gets a lot of 'garage time', with Scarlett sleeping roughly 10 hours per day. I charge when the range gets down to between 45 and 85 miles indicated, and charge up to 80%. I've charged to 100% only four or five times so far, and always just before a trip. And, since we live in the Phoenix area, we have some 'VERY' hot weather (50 days this year over 110), which affects not only people, but Scarlett's battery. When we return home from errands, the temperature in the garage is still in the mid to high 90's, so Scarlett cools down slowly and uses quite a bit of energy for extended periods to cool down the battery. [Incidentally, the Cabin Overheat Protection feature is awesome.]

Following the logic we're discussing, BMS has plenty of time to recalculate range. So, I believe that Scarlett is telling me as close to the truth as it can. I charged last night, and 80% tells me that I have 268 miles. If we start with the 315 number, times 80%, that number should be 252. So, Scarlett is saying I really have 85%. Nice!

Any holes in the logic here?

The hole may be this: are you sure it's exactly 80% with 268 miles reported? Probably not, it's really hard to get it to hit 80% exactly.

isn’t battery/range also affected by temperatures? Especially reduced range in cold weather?

Yes. Up to about 3% before you see the "snowflake", and presumably more after that. It's gradual.

My LR AWD range has been steadily declining over the past 2 years and I'm nearly at the level the OP has at 272 miles at 100% SOC. I've tried lots of "calibrations" with no luck. However, this information is promising so I'll try this too with some hope. My commute is 130 miles roundtrip so I usually charge daily but I will try to rest the battery at different SOC's and see if it helps. Thank you for this info. Here's hoping.

Edit, forgot to mention, I just had my battery breather valves replaces this week due to unusual loud pops when supercharging. Coincidentally, I lost another 8 miles of range shortly after. Unsure if it had anything to do with it.

Replacing the breather valves would have nothing to do with your battery capacity, measured or real. I don't think they even do a high-voltage disconnect for this procedure, so your car may literally not notice anything being done to it.

So, to me, that is another trade-off. It sounds like you could be slowly degrading your battery more so that you can get better capacity readings from the BMS.
I tend to try to keep my battery in the 40%-80% range nearly all the time and only go above or below for a rare long distance road trip.

Personally, if I felt my range indicator was to drift too far from (what I think is) battery reality, I would do a one time skip on charging, and one time charge to 90% just to get more readings, but I wouldn't make it a habit of letting it get down to 20% on a regular basis.

This is absolutely the case and understanding outside this thread, yes. Most "calibration" procedures, recommended either here or by Tesla, do technically wear the battery more than otherwise.

I guess I don't understand. If there is really a suggested regime for charging to make the battery last as long as possible it should be in the user manual. If not, why not? Either Tesla stands behind the charging regime or they don't. We shouldn't have to guess at this. Here is an idea - put an option on the menu that forces the Tesla to do whatever it has to correctly estimate the true range of the current battery (hey Tesla could call this a new feature!).

If it's not made clear by this thread, there are too many variables at play to make a blanket suggestion for charging habits that is beneficial to everyone.

The singular clear thing is that charging above 90% routinely is almost never good, and that is the one recommendation they're aggressive about (the car will even warn you if you charge to 100% multiple times in a row). Anything further recommendation needs to account for too many local variables and personal use-cases.

Agreed. It appears to be rather too variable for people to fully comprehend. People aren't used to the size of their gas tank changing with temperature, for example.

But I'd argue that when the range shows a particular number, it really is an extremely accurate estimate (within 1-2% I would think, not including the buffer) of actual energy available at that point in time at that pack temperature.



I think we generally understand from SMT that (for Model 3) there is a 4.5% buffer below 0 rated miles, which is part of the available pack energy, which is not *exactly* shown on the display. But this manifests as each rated mile containing roughly 234Wh/rmi (pre-2020 AWD M3) rather than 245Wh/rmi (which is the actual total available energy content of the battery, including the buffer, when you take the number of rated miles at 100% and multiply by that scalar). These values differ by 4.5% of course. This results in about 4.5% of pack energy being available still when you hit 0 rated miles. Hard to say how much of that is truly usable though. Don't want to press that accelerator too hard at that point or you'll get a brownout (hopefully not in your shorts though)!

Tesla definitely doesn't want to have the car shutting down when you hit 0 rated miles (or slightly before). That seems to me to be the reason for the buffer.

I suspect the unreliability of the below-0 capacity is due to voltage sag. They start cutting max power heavily at low SoC to prevent voltage sag from going outside the boundaries of heavy damage (made worse by the reality of higher sag at low SoC). My guess is they cut the battery out the moment a cell exceeds or touches a voltage threshold. You'd be especially at the mercy of cell variances at this point too.

 

[AZAV8R]

Your polite approach to disagreeing tells me that I picked the right place to land after escaping the Tesla forum.

Great info. I'm trying to get a deeper level of knowledge of my M3; I don't intend to act on every idea. The bottom line on this for me is that it is not an issue about actual range, but one of calculated range.

So, it's keep calm and drive on!

 

[Battpower]

The bleed resistor thing sounds all wrong. Balancing setups generally aren't like this (maybe never?), for many reasons:

• The bleed resistors, for balancing, cannot (reasonably) be permanently draining
  • By definition, the battery is not open-circuit if there's a reasonable load across any of the cells (e.g. for balancing)
• Being the "primary cause" of vampire drain measured in the wild would require some unrealistic values
  • Stats says ~60W median for LR. 96 series bricks means each brick drains 0.625W
  • Implies chonky 1W resistors. These would be visible on the BMS boards. I see no such resistors. I don't even see 1/4W ones.
  • At 4.0V (reasonable guess of average SoC, ~73%), that implies a ~25 Ohm resistor. That is a very, very low value for a "bleed" resistor.
• If the bleed resistors were 10x higher (and always engaged), voltage would reach steady state faster, not slower. Higher resistance equals less power draw. Less power draw sags the battery voltage less. Less sag means being closer to steady state or "open-circuit".
  • That would also imply 2.5 Ohm "bleed resistors" on S/X. This is more into current shunt territory than bleeds, and would indeed cause massive vampire drain if always engaged. But S/X are not that bad.
• Most importantly, bleeding all bricks simultaneously just wouldn't be an effective way to balance - no balance is actually occurring this way, just a fixed drain no matter what the capacity of that brick is, which would actually induce imbalance over time.

These are the bleed resistors from a Model S. 4 x 158 ohm (the ones marked 1580 in 6 rows). 4 resistors effectively balance 1 brick of parallel cells. In the S these are then in modules of 6 bricks, so this picture is of the balancing resistors for one module of bricks. They are tiny resistors and on the face of it totally not up to the task of balancing 70 - 100kwh of cells (although of course there are around 15 such boards for a whole battery.)

As @camalaio points out, you don't want to be wasting energy bleeding it off as heat, and thankfully if the battery is in overall good shape, energy will be evenly distributed accross all the cells and the electro-chemical state of all the cells will be closely enough matched that they absorb and release energy similarly, and so the balancing circuits will have little to do and no energy needs to be 'wasted'. Even when these resistors are connected in circuit, they will draw maybe 100mA, so not much power in the overall scheme of things. Over a period of time you just need the balancing process to take into account differences in energy handling due to intrinsic differences between individual cells.

Now, stabilised could've meant "balanced" I suppose, which kind of makes sense in the post? But this doesn't seem right?

'Balanced' is a somewhat ambiguous term, especially if you don't state what it is that's balanced. This is correct:

There's much for the BMS to learn during a drive (changes during discharge and regen can reveal a lot), but a non-sagged open-circuit voltage is fairly representative of the battery state especially when battery temperature is also known (and indeed, it is to the car).

This is a very 'dynamic' system, with ever changing loads and stresses, and at the electro-chemical level there is loads going on right at the limit of understanding. So when you put a heavy load on the battery, differences between bricks means that their voltages will all be different while under load. This does show a transient imbalance (or maybe better 'inequality') of voltage, but not really a meaningful imbalance in the battery.

A good battery will have electro-chemical uniformity / consistency allowing it to self-maintain even energy distribution without the need for external balancing. Of course, perfection is impossible, so judicious bleeding off of energy aims to keep the energy 'balanced', 'equalized', or 'evenly distributed'. At the start of a charge, the BMS knows which bricks are going to absorb more energy, so it will turn on the corresponding resistors to allow some (small amount of) charge to bypass them. Conversely, all the 'other' (lower energy) bricks can be helped slightly during discharge by shunting some current through their resistors. So you can effectively equalize energy distribution during charging and discharging.

Keep in mind also that in one sense, not one single cell is ever open circuit even if the HV isolator is pulled. Albeit microscopic, there will be current flowing all the time in the pack as temperature changes, again due to differences in cells. Every cell is permanently wired directly in parallel with other cells (unless its invidual fuse blows when it ceases to be part of the battery).

I find 3+ hours to stabilise voltages incredibly hard to believe

The stabilizing of voltage (which involves every cell) is due to charge equlalizing between parrallel connected cells. Every cell is SLIGHTLY different and when the only currents flowing are those imbetween parallel cells, each brick voltage will stabilize / normalize towards the point as which the electro-chemical potential of all the cells is the same. Since the 'electro-chemical' potential keeps reducing during 'settling', so too does the rate of settling. It could take a very long time, but we are talking very small differences!

Especially in the pandemic where we leave the car unplugged at various percentages now, it has more of a chance to gather more readings.

The result of that? The reported capacity plummeted nearly all at once, no gain.

The BMS needs to see everything. Charge, discharge, heavy / light loads, settling times.... the lot. Not driving means it has loads of time watching 'settling' but no corresponding energy use the effects of which are worth gathering data about. I'm sure Tesla gather as much useful data as possible to guide the battery management process. EM has said 'good for the car to just leave it plugged in on AC'. This is likely correct as it leaves the car to decide exactly what it needs to do, including a top-up charge to whatever SOC limit is set.

Small effective capacity gains may happen via balancing, but that's a whole separate topic

I think there is an important distinction needs making between batteries that are basically in' good shape' and capable of doing the required job, and batteries containing bricks / cells that for whatever reason have a significantly degraded and become sufficiently 'different' in their characteristics that the balancing systems can't keep the pack usefully uniform / coherent in its energy storage and release function. If you reach that situation then whatever you do, it's just trying to polish the proverbial turd. Hopefully M3 / MY cars won't see this for some time but there is plenty of evidence amongst older / heavily used MS.

 

[Battpower]

The bleed resistor thing sounds all wrong. Balancing setups generally aren't like this (maybe never?), for many reasons:

• The bleed resistors, for balancing, cannot (reasonably) be permanently draining
  • By definition, the battery is not open-circuit if there's a reasonable load across any of the cells (e.g. for balancing)
• Being the "primary cause" of vampire drain measured in the wild would require some unrealistic values
  • Stats says ~60W median for LR. 96 series bricks means each brick drains 0.625W
  • Implies chonky 1W resistors. These would be visible on the BMS boards. I see no such resistors. I don't even see 1/4W ones.

I tried to find a picture of the disipating components for the M3 and found this:

model-3-battery-pack-bms - TESLARATI

but am not sure what's what.

Unless the dissipating components have some provision made for their dissipation needs, (in Model S they are internal to each module so presumably experience whatever the internal module temp is) I can see that their ability to function as required could be compromised.

I wonder if there isn't a better approach to balancing using ultra capacitors? This would seem especially useful in an application with high transients especially while driving and would allow high level regen even at low temperatures. It could also allow charge to be shuttled from one brick to another in an active manner rather than passively bleeding off energy - even if when everything is in good shape you don't actually have much energy balancing to do.

 

[Tholland]

I guess I don't understand. If there is really a suggested regime for charging to make the battery last as long as possible it should be in the user manual. If not, why not? Either Tesla stands behind the charging regime or they don't. We shouldn't have to guess at this. Here is an idea - put an option on the menu that forces the Tesla to do whatever it has to correctly estimate the true range of the current battery (hey Tesla could call this a new feature!).

This... this is what I have been saying. For some of us we like to tinker and find out stuff and explore. The majority DOES NOT! This should not that hard to figure out as the consumer. The car is probably the smartest car on the road. The car can for sure be fixed to where it gets the rated range correct or at least closer to normal reading. Again, Tesla knows what they’re doing. The car has 3 different calculation it uses for stuff. I just think they need to make the displayed ranged more accurate period.

 

[Tholland]

Yeah. The only reason I keep coming back and discussing these things here is that there seems to be a persistent idea out there amongst some Tesla owners that somehow the rated miles reduction observed on every Tesla vehicle (and every EV in general!) is somehow "not real" or "temporary." But I think we've proved elsewhere here that this is definitely not true. Measured carefully via means other than the car itself, any owner can demonstrate that cars showing lower rated miles take less energy to fully charge. That indicates definitively that vehicles with fewer rated miles at 100% contain less available energy after being fully charged. QED. (I guess you could argue that cars with lower rated miles have lower charging overhead but that would make no sense.) But somehow the idea that this is just an estimate (to be clear: it is an estimate, but accurate within 1-2%, probably) persists!!! It's weird!

I swear I missed reading your explanation lol. Some of the best out there

 

[Wennfred]

Day 2 of deep sleep and the Graph is showing upticks in the right direction. Charged to 95% before deep sleep. Last 2 ticks are 29th & 30th. Prior to this no sleep due to Sentry mode:

 

[SomeJoe7777]

There's some really really good advice in the OP, surrounded by some really false details, and also a bad suggestion or two. This does not eliminate the fact there are good points though, which I've summarised at the bottom.

I struggled with posting this, as it seems combative and/or argumentative? But that isn't my intent. @SomeJoe7777, this ain't your fault for "getting wrong" so please don't see it that way. Seems like you were fed a bad explanation IMO. This actually happens a lot from Tesla Service employees, unfortunately (as they're pressured into offering some explanation with their current understanding). You brought new information to us, which is very appreciated!

I appreciate that and agree with you that I can't rely on all of the information I was given. Indeed while much of it is useful, some of it doesn't seem 100% correct.

The bleed resistor thing sounds all wrong. Balancing setups generally aren't like this (maybe never?), for many reasons:

• The bleed resistors, for balancing, cannot (reasonably) be permanently draining
  • By definition, the battery is not open-circuit if there's a reasonable load across any of the cells (e.g. for balancing)
• Being the "primary cause" of vampire drain measured in the wild would require some unrealistic values
  • Stats says ~60W median for LR. 96 series bricks means each brick drains 0.625W
  • Implies chonky 1W resistors. These would be visible on the BMS boards. I see no such resistors. I don't even see 1/4W ones.
  • At 4.0V (reasonable guess of average SoC, ~73%), that implies a ~25 Ohm resistor. That is a very, very low value for a "bleed" resistor.
• If the bleed resistors were 10x higher (and always engaged), voltage would reach steady state faster, not slower. Higher resistance equals less power draw. Less power draw sags the battery voltage less. Less sag means being closer to steady state or "open-circuit".
  • That would also imply 2.5 Ohm "bleed resistors" on S/X. This is more into current shunt territory than bleeds, and would indeed cause massive vampire drain if always engaged. But S/X are not that bad.
• Most importantly, bleeding all bricks simultaneously just wouldn't be an effective way to balance - no balance is actually occurring this way, just a fixed drain no matter what the capacity of that brick is, which would actually induce imbalance over time.

I agree that the resistor explanation is a lot of voodoo.

So let me clarify that when I'm talking about vampire drain in this context, I'm speaking of the inherent drain inside the main pack itself. The 60W median you're speaking of is the drain for the entire vehicle. That includes energy use that's far larger than the internal balancing resistors, i.e. charging the 12V via the DC-DC converter. So your calculations that show a very low and impractical resistor values I don't think are accurate.

I do wish I knew more of the engineering design choices behind the bleed resistors and we could estimate better what is going on.

We can see from the picture posted by @Battpower that there are 158 ohm resistors in the Model S/X pack. Without looking at the back of the board, I can't tell whether these are in parallel, series, or some combination so I don't know the exact resistance presented across each module. But if the Tesla tech was accurate on the one point that the Model 3 battery aims to reduce the drain through the balancing resistors, then the resistors in the Model 3/Y packs should be higher in value.

While my post may indeed raise more questions than answers about the battery construction (and I wouldn't have posted if all I had was just the Tesla tech's information) the results speak for themselves. How bad does the BMS have to be at range estimation if I can gain a full 20 miles in indicated range just by changing my charging habits? I think this is a very significant finding.

And don't do these:

• Don't: Charge to 100% to "balance". This happens at lower percentages anyways as well, and balancing to an uncommon state actually offsets it in a non-ideal way. Balancing would also take a lot of time, so doing this right before a trip doesn't accomplish that anyways.
• Don't: Skip charging to provide more data points. While I've found some vampire drain benefits to being unplugged, not having the capacity when you suddenly find need for it is not good. There is no sense in stranding yourself because you left the car unplugged at 20% just so the battery meter is very very slightly more accurate. That's like 50mi of range of a brand new SR+ in ideal conditions on flat ground.
• Don't: Take TeslaFi/Stats/etc. graphs as accurate. There's so many problems with the way these report capacity in general, and can paint pictures that don't reflect reality.
• Don't: Take Tesla Service's guidance on everything regarding batteries. Some do have some generally good advice, but some have their own wild theories. They are often not battery experts, they are mechanics. That said, don't take some internet dude's advice either, me included!

I agree with you on most of these, but I'll point out a few things:

1. If you're going to charge to 100% for range, like for a road trip, then let the car charge fully. This may take a while. Incomplete charges to 100% where the balancing doesn't finish can make the calibration worse.
2. Obviously, don't strand yourself by leaving the car with a low charge. For my family, we have two Model 3's, and my wife's is nearly always at 80%, so we can always use hers if we need to go somewhere and my Model 3 doesn't have sufficient charge. Furthermore, we have a supercharger about 4 miles away from us, so we can use that if required. Indeed make sure you have a plan if you want to leave your car in a low state of charge.
3. I didn't make my battery meter slightly more accurate, I made it a LOT more accurate. Like 8% of total capacity more accurate. That's very significant.
4. While the 3rd party tools may have some idiosyncracies, all of their data is from the car. It may not be presented in the best way, but it's not false. And, comparisons that you make within the same tool can indeed tell you things. If TeslaFi's 270 mile estimate when my battery was at it's low point wasn't precisely accurate, that's OK, because we can assume that the same inaccuracies are present in the current reading of 290 miles. I gained 20 miles in this tool, calculate from the car's data.

I do hope we can eventually answer a lot of these questions, but without more teardown and analysis of the Model 3 pack, I don't see it happening. We can banter back and forth here until the next blue moon, but still may not get anywhere without more facts.

 

[dhrivnak]

After reading this thread, I agree with SomeJoe777's conclusions but I think there is a much easier way to get there. I am a retired engineer, who has build several EV's, owned a Roadster for 10 years, a Model 3 for 2 1/2 years (47,000 miles) and in all have over 135,000 gas free miles under my belt. I charge each day to 90% and about 4 times a year take a trip where I charge to 100% and then the car normally sets for a few hours as I set the charge at night and the car fully charges while I sleep and then I head off in the morning. As Joe777 alluded to this ensures my battery stays balanced AND calibrated. I learned with the Roadster (and parameters may be different) that there is no balancing below 82% charge and only partial balancing at the default 83% charge level. We were schooled to occasionally range charge for full balancing and calibration and that served me well for 10 years. The reason is there is very little voltage difference in lithium batteries between 20 and 80% charge level. So if you routinely charge to say 70% there is not enough voltage difference for balancing to occur. You only see differences at the extreme levels, below 10% and above 90%. So my default charge level is 90% and that is why I do not stress about an occasional 100% charge. The BMS needs to see both the top and the bottom on occasion and if it does not the estimates, being conservative will drop your range. Part of this is real as a pack is only as good as the weakest brick. And if your pack is out of balance that low brick will not be brought in line and it will limit your range. It is also true that if you always or eve frequently charge to 100% that too will damage your battery.

Now look at the second graph of my Model 3 over the past 47,000 miles. My range is actually up 1 miles if you compare my first 15 readings (278.2) versus the last 15 readings (279.4). One could argue I am actually down 4.5% as I did get a 5% range boost from Tesla during this time. But I have also noticed the average can jump up or down several miles after a firmware update. But If you look at that second graph I think you will find loss in capacity is negligible.

So my advice to those who stress about range, or loss of range. Charge daily to 90%. On the few times you could use 100% use it. And if you occasionally go below 5% that too is fine as the BMS needs to see both the top and the bottom for it to be accurate.

An analogy if you like at the bottom.

Lets say you start off on a hike to an overlook 3 miles away. Knowing your pace of 2000 steps/mile that is 6000 steps. So you start off and after 4000 steps, you realize you need your hiking stick that you set down on a break so you hike back 3000 steps. Then you start back and after 3500 steps you realize you dropped your jacket out of your pack and turn around again and take 1500 steps back. Then you resume your hike. Using math, you should still be 3000 steps from the overlook. But are you what if your pace today is 2100 steps per mile, or the trail was more rocky than normal so you had to take a lot of little steps. The only way to really know is to get to the overlook or back to the start. And once there you can now calibrate your position and for the first time in many hours you for sure know where you are at. The rest of the day was just educated guesses. If the BMS does not know the start or end, you are left with estimates and guesses. If those estimates are estimates of estimates for over a year the accuracy is fair at best.

 

[TEG]

FYI:

cell balancing

Tesla Model 3 - NextGen Battery - EVTV Motor Verks

 

[SageBrush]

The bottom line on this for me is that it is not an issue about actual range, but one of calculated range.

Spot on.

I am waiting for my canbus adapter to arrive by mail and then I'll have 'scan my Tesla' to compare actual cell voltages with the rated miles display in the car. It should give me early warning if the calibration is out of whack.

 

[Phlier]

@camalaio You handled being "that guy" very, very well. Seems like every time you post, I learn something.

 

[Dave EV]

But if the Tesla tech was accurate on the one point that the Model 3 battery aims to reduce the drain through the balancing resistors, then the resistors in the Model 3/Y packs should be higher in value.

As mentioned earlier, changing the value of the balance resistors makes no sense. They are only turned on/off as necessary, so changing the value will make no big difference in efficiency unless there are other changes that go with it. The energy dissipated by the resistors is only whatever energy required to balance the pack. The values only change the speed at which the modules are bled down.

 

[thebooker]

The only reason I keep coming back and discussing these things here is that there seems to be a persistent idea out there amongst some Tesla owners that somehow the rated miles reduction observed on every Tesla vehicle (and every EV in general!) is somehow "not real" or "temporary."

As in those who say "you really haven't lost range, just switch the display to percentage"?

Exploring that idea: When new, my midrange M3 had a range of 260 miles. I charge it to 100% and then look at the predicted range I see it is 260 miles. I then make a trip of exactly 260 miles under ideal conditions. Sure enough, when I look at the display I see 0 miles and 0%.

Now, two years later, my display tells me that when charged to 100% I can go just 230 miles (pretty close to my current car). So, I charge to 100% and take off and drive. When the display says 0%, I stop or(or car quits). At that point my M3 has been ringing alarm bells for some time. When I switch the display to miles, am I not going to see I've only gone 230 miles?

So, I guess my basic question is, what is battery voltage at 100% and at 0% for the second case? I assume for the "new car" case the voltages would be ( from graph provided later by dhrivnak )58.2 and 44 volts. My question is: Wouldn't those two voltages be different for my two year old car?

 

[SageBrush]

So my advice to those who stress about range, or loss of range. Charge daily to 90%.

I am not a fan of charging to high SoC in the summer unless needed; and I don't see any advantage to daily charging unless needed since as OP mentions this reduces the number of OCV data points the car can use for its calibration curve.

I'll give my car some 90% SoC data points to chew on when it is cooler. As a WAG perhaps when the pack is ~ 20C since I presume that is close to manufacturing test conditions.

 

[dhrivnak]

....I don't see any advantage to charging daily...

Except Tesla says we should always keep the car plugged in.

from the Model 3 Owners manual. “The most important way to preserve the Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. “

I wish we had more details but until then I plan to keep my car plugged in.

 

[Wennfred]

Except Tesla says we should always keep the car plugged in.

from the Model 3 Owners manual. “The most important way to preserve the Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. “

I wish we had more details but until then I plan to keep my car plugged in.

I believed that too, always plugged in and charged to 90% but after taking a big battery dump and seeing a downward trend it was time to rethink that. I mean let it sit for a few days so that the battery goes into a deep sleep over night and Let it do it’s balancing and after the 3rd or 4th day hit it again with a charge. Day 2 and I’m already seeing an uptick, will keeping doing this for a week and report back.

Fred