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How often do you charge?

How often do you charge?

  • Only DC fast charge/supercharger

    Votes: 4 3.9%
  • Every day

    Votes: 36 35.3%
  • Every other day

    Votes: 17 16.7%
  • When the battery gets low

    Votes: 28 27.5%
  • Can't get enough juice (always plugged in)

    Votes: 17 16.7%

  • Total voters
    102
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The owner manual encourages frequent charging as much as possible and there's no advantage in waiting.



Service Center is recommending charging at 90% and not below 90% if you can.

They told us 80% at pickup. I've seen other mentions of 80% before too.

I put the car on charge at night but I try to work a charge in during my lunch break on one of the free chargers in Scotland. It's a nice little ritual really. I save little bit of money and I get to sit and read a book or watch netflix or whatever.
 
Do you have a source for this? I am not familiar with a need to charge to 100% ever or to balance the cells?

Balancing works by diverting the excess charge current around any cell which is already well charged. Conventionally this is done by clamping the charge voltage of each bank (so it only happens on the final constant-voltage part of the charge cycle). Thus once the whole bank is at the top end of the nominal voltage, you will be as balanced as you can be. To some extent, this can probably be done in the 50-90% charge range too if so designed, but it can't be as effective as at the top of the range due to the uncertainty around how charged a half-full cell really is.

Balance is significant because as soon as one bank reaches the minimum, the whole battery needs to be treated as discharged. There is no practical way to balance during discharge (not that it is impossible, it is just far easier to do on the charge cycle). I don't believe there is any significant stress or inefficiency caused by leaving the stack unbalanced when you're not draining it fully, you just need to be making best use of the weakest cell to see the full potential capacity, and maybe get good SOC estimates.

For example, my current hybrid occasionally re-calibrates it's state of charge estimate when one cell hits the cut-off voltage - it can drop from 70% to 0 charge when it does this (but the BMS design is well over 10 years old)
 
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Balancing works by diverting the excess charge current around any cell which is already well charged. Conventionally this is done by clamping the charge voltage of each bank (so it only happens on the final constant-voltage part of the charge cycle). Thus once the whole bank is at the top end of the nominal voltage, you will be as balanced as you can be. To some extent, this can probably be done in the 50-90% charge range too if so designed, but it can't be as effective as at the top of the range due to the uncertainty around how charged a half-full cell really is.

Balance is significant because as soon as one bank reaches the minimum, the whole battery needs to be treated as discharged. There is no practical way to balance during discharge (not that it is impossible, it is just far easier to do on the charge cycle). I don't believe there is any significant stress or inefficiency caused by leaving the stack unbalanced when you're not draining it fully, you just need to be making best use of the weakest cell to see the full potential capacity, and maybe get good SOC estimates.

For example, my current hybrid occasionally re-calibrates it's state of charge estimate when one cell hits the cut-off voltage - it can drop from 70% to 0 charge when it does this (but the BMS design is well over 10 years old)

Why would the battery not being balanced be bad though? Don't think it does the battery any actual harm, just less accurate readings?
 
I work at home too. Picked up my Model 3 on Sunday and charged overnight to 90% (or what looks like 90% where the white line is), up to approx 280 miles range. Only driven a few miles each day since so it’s currently sitting at 255 miles range. I’ve not plugged in again since Sunday night and don’t see any need to do so until it’s down to about 50%.

I’ve assumed that there is no issue leaving the car for a few days or a week between charges, even though the Tesla mantra seems to be that “a plugged in Tesla is a happy Tesla”. Not sure I see the point of plugging in at home to go from 255 to 280 miles when I’m not planning a long trip the following day.
 
Do you have a source for this? I am not familiar with a need to charge to 100% ever or to balance the cells?
The most common view I can find now seems to be only charge to 100% if you really need to and even then time it to get to 100% just before setting off so its not held at 100% for long periods.
My original source was the user manual for the Leaf.

However, reading this article:

BU-803a: Cell Matching and Balancing – Battery University

states two things: that balancing occurs at 80% charge and that EVs have active cell balancing anyway, so it seems to be unnecessary.

I won’t bother any more! We’re always learning...
 
90 is too high and definitely will get much more degradation than 80.
Interesting that the poll so far is very varied.

They told us 80% at pickup. I've seen other mentions of 80% before too.

I put the car on charge at night but I try to work a charge in during my lunch break on one of the free chargers in Scotland. It's a nice little ritual really. I save little bit of money and I get to sit and read a book or watch netflix or whatever.

Interesting vid here. Chap keeps it between 20-80%, says Tesla checked his battery degradation after a year and it’s one of the least degraded they’ve seen. It also goes into some detail on the SoC % v. Miles calc

That video may be a verbal personal instruction but not a company-wide official policy.

There have been quite a few reports that Service Centers have written down the words "poor charging habit" for those who charged 80% and they also wrote down the recommendation to charge 90% on their Service Receipts.

The video below didn't believe those reports and found out on her own by bringing her car in and that it's true.

upload_2019-9-13_11-54-0-png.454293
 
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Why would the battery not being balanced be bad though? Don't think it does the battery any actual harm, just less accurate readings?

All I can think is possibly some cells being supercharged when already at max SOC - but the balance management ought to detect this and back off the rate of charge to something it can handle. Probably a 'legacy' issue rather than something to worry about.
 
Why would the battery not being balanced be bad though? Don't think it does the battery any actual harm, just less accurate readings?

There are 2 different issues here:

1) Inaccurate battery gauge due to inaccurate calculation is not harmful:

Such as the battery gauge says 80% but it is actually 90%.

You just think the battery is more depleted but it is not.

2) Unbalanced cells are harmful:

BU-803a: Cell Matching and Balancing – Battery University

The more unbalanced the pack is, the worse it gets. The purple line is way down after 18 cycles while the red one is minimally affected below:

cell-balance.jpg
 
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Is there any logic with the feeling that if you have a rigid charge routine you will wear out the same cells over over. Again no knowledge but it feels like now and again it would be good to run the battery down to a lower than typical percentage to ‘slosh’ the electric around to the lesser used cells.

:confused:
 
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Reactions: Roy W.
If you are plugged in does it trickle charge after it has topped up or just top up every now and again?
If it keeps topping up small amounts that's quite bad for the battery like leaving your phone plugged in after it's finished charging.
 
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If you are plugged in does it trickle charge after it has topped up or just top up every now and again?
If it keeps topping up small amounts that's quite bad for the battery like leaving your phone plugged in after it's finished charging.
You can't think of EV batteries like phone batteries.

EV batteries are constantly "topping up" using regen while you're driving.
 
I have seen some laboratory based work on LI ion batteries that shows that charging to 100% is terrible for degradation and that that impact drops off exponentially with charge so 90 is much better than 100% and 80 is a bit better than 90 etc etc. doubt I can find it now but I will look.
I am pretty sure this holds true for all current Li but what I think we don't know is when we say 100% what is it really? its not 100% that would be crazy given how that affects degradation. Tesla would be shooting themselves in the foot if they allowed that. They clearly have less reserve capacity than other makers but it's not zero. The fact that they software update vehicles in hurricane zones to give them more range shows that I think.
So given that 100% is not 100% and the impact is exponential I can see why 90% (probably really 85-80%) would be OK. What I can't explain is why 90 might actually be described as better than 80 and 80 is actually considered "poor charging habit" There may be a legit technical reason but its not obvious what that might be?
 
Why would the battery not being balanced be bad though? Don't think it does the battery any actual harm, just less accurate readings?

Traditionally, a battery bank will only have as much power as the weakest cell. The unbalanced cell get more stress, then fails earlier.

Tesla has a sophisticated battery management system, so this is much less than an issue that with other systems.

I have never seen any authoritative information regarding a requirement for balancing Tesla batteries. Random Internet strangers are not authoritative.
 
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I fly FPV (First Person view) Freestyle drones and use LIPO (lithium polymer) cells "Batteries" - (1300mah or 1500mah 4s & 6s if you know your batteries!)

We use these batteries (Similar voltages to the 18650/21700 in the teslas) between Voltages of 3.3volts to 4.2v (max) and the battery pack cells are in parallel so these cells can balance when they approach the 4.2v when charging. The Chargers we use does this balance for us using a balance lead on the battery which is connected to each cell. The balance to the cells happens at the top end of each charge and this is where the charge process becomes very slow!

There are batteries that have HV (High Voltage) chemistry in them and you can charge these upto 4.35v.

The 4s or 6s mentioned above denotes the number of cells (in a battery) in parallel to each other (4s = 4 cells @ 4.2v per cell, max charge each). Tesla battery packs are in both parallel & series to give you your battery capacity and Voltage. (not sure on the configuration)

Example:

Cells have a capacity and this is denoted as the example above "1300mah". (milliamp Hour) or 1.3ah (amp hour)

If a battery with 4 cells are in parallel (all batteries joined to gether) and have a 1300mah capacity to each cell, then the total battery capacity is still 1300mah but the voltage has increased to 16.8v (4 x 4.2v max charge). - "This would make your car faster but not go very far"

If they were in serial (in a daisy chain) then the capacity would be 5200mah but the voltage is only 4.2v (4 x 1300mah capacity) - "This would make your car slower but go much further than the parallel version"

So a balance between the 2 examples above is needed!
Also amps generate heat! so higher voltage and lower amps is better. It also looks after your motors. High volts - low amps!


We can fly these down to 3v but the battery cells can become out of sync/damaged so the 3.3v is kind of a buffer and most fly no more lower than this to preserve the batteries. I belive Tesla use this to have a buffer at the end. The bottom end of the battery voltage, below 3.3v the drones become less punchy, slouchy and slow, so the 3.3 to 4.2v the drone does not suffer this.

If a battery cell becomes weak/damaged it effects the rest of the pack by pulling these voltages down as well. Hence the need to balance and keep each cell the same (0.1v difference is fine)

The 18650/21700 batteries i believe can allow upto 20-30amp draw on each (thats the max amps per battery a driver might pull punching the fast pedal), but these batteries only charge at 0.5c rating. So a single 2500mah 21700 battery can take 2hrs to fully charge. But seems tesla battery tech can ramp that up to 1c maybe more? charge rate (1c is denoted as 1hr to charge to the advertised battery capacity - 2500mah battery needs 2.5amps to fully charge in 1 hour from around 3.0/3.3v to 4.2v). 2c takes half the time to charge and visa versa!

So balancing a battery pack is needed to keep them in harmony. And ofcourse to see if any problems arise as you will notice this quicker with a well maintained balanced battery than 1 that is not. :)

Although im not sure how often! :/

Also you are more than welcome to put me right if anything is wrong! :)