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Charge Cycles: A terrible metric

How often do you charge your Tesla?


  • Total voters
    46

Baldey

Member
Oct 15, 2019
5
0
Colorado
Hey guys, so this is my first post... I have had my Model 3 for about three months, but I am kind of antisocial :p Loving the car so far [attached is a baby picture], but...
IMG_20190716_155632.jpg

Perhaps it is my fault for being naive enough as to not even own a cell phone in 2019 (i'm lucky enough my company provides one), but my limited knowledge of lithium batteries led me to assume that optimizing for less charging cycles would improve my battery longevity. So i'd always charge up to 90% and drain to at least below 50 miles every time, feeling proud of myself every time i beat my previous charging record. I think my record to date is 44 kWh in one charge! But..

Recently, i've come across this article: https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries . Quite lengthy, but luckily the interesting information is near the top. If you take a look at the DoD (Depth of discharge chart) , you will see that a LiPO cell will last 25 times longer if discharged by 10% as opposed to 100% (compared to the expected 10x difference). Or 10 times longer when discharged by 20% as opposed to 80% (compared to the expected 4x difference). So according to this chart, is is more than twice as healthy for your battery to charge your Tesla every day when you've barely used it, then it is once/twice a week when its near empty or even below half.

So is my conclusion true, should i charge my car every night to make my battery last longer? Does anyone know about this?
Thanks,
-Yev
 

Baldey

Member
Oct 15, 2019
5
0
Colorado
Sorry, i meant to say that a LiPO cell will have 25 times the cycles if discharged by 10% as opposed to 100% (compared to the expected 10x difference) . they are 90% smaller cycles though, so the battery actually lasts 2.5 times longer. Which is a huge difference..
[I can't edit the original post?]
 

ZOMGVTEK

Member
May 19, 2015
559
442
'Merica
This is surprisingly a common way for people to interpret charge cycles. A charge cycle is considered to be replacing the energy the pack holds from 0-100%. So this means it will take 5 charges from 60-80% to get one full cycle. This is more complex of an issue than you might initially assume, but shallow discharges are quite a bit easier on the battery than deep ones. This doesn't really tell the whole story. The question is how much it matters, and what strain is put on the remainder of the vehicle as a result of more frequent shallow discharges. The car will have more wear elsewhere with being plugged in more frequently. In addition to this, the thermal cycling will accelerate wear on some components. So there is kinda a balance here. You don't really want to plug in to put that 1% back in, but 10-20% is probably sensible if its convenient.

Generally speaking, plugging in every day if you use more than 10% a day is probably 'best'. If you use single digits, maybe every other day. But its really unlikely to be a big deal. I wouldn't worry about it too much. I would expect outright failure of some component is more likely to warrant a pack replacement before degradation hits a level that's considered unacceptable.
 
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derotam

Member
Oct 31, 2018
847
795
Oak Hill, VA
This question or variations thereof get asked a lot and everyone will give you a plethora of information. You will also get a plethora of opinions because everyone has one, just like everyone has an...ok anyway...I'll give you my opinion...Just remember also, there is always more than one way to skin a cat and there isn't a one size fits all solution for everyone.

The manual as stated in post #3 above makes certain statements which aren't all that informative and a couple of which are in my opinion not accurate. I will not go into this at this time.

Personally what I do is set my charge level to 70% normally unless I need additional range for a specific scenario. I will run it down to approx 30% before I plug it in. As previously stated by ZOMVGTEC, it is a complex issue and the balance varies from situation to situation. You have the battery, the charge port, the mobile connector, the wall plug...etc that is being exercised every time you charge. If you go on multiple small trips every day from your home and you plug in every time you get home, you are adding wear and tear on the physical connections, in my opinion, unnecessarily.

Li-Ion batteries don't like extremes, so going to and staying at low or high SOC is more stress on the battery.

There are a lot of ranges that float around, 30/70, 20/80, 30/60 etc. The difference between them in terms of battery longevity is in my opinion negligible. If you want the battery to last the longest, set it at 50% plugged in and then never drive the car...but then you aren't "grinning"
 

KenC

Active Member
Sep 4, 2018
3,748
3,483
Maine
This question or variations thereof get asked a lot and everyone will give you a plethora of information. You will also get a plethora of opinions because everyone has one, just like everyone has an...ok anyway...I'll give you my opinion...Just remember also, there is always more than one way to skin a cat and there isn't a one size fits all solution for everyone.

The manual as stated in post #3 above makes certain statements which aren't all that informative and a couple of which are in my opinion not accurate. I will not go into this at this time.

Personally what I do is set my charge level to 70% normally unless I need additional range for a specific scenario. I will run it down to approx 30% before I plug it in. As previously stated by ZOMVGTEC, it is a complex issue and the balance varies from situation to situation. You have the battery, the charge port, the mobile connector, the wall plug...etc that is being exercised every time you charge. If you go on multiple small trips every day from your home and you plug in every time you get home, you are adding wear and tear on the physical connections, in my opinion, unnecessarily.

Li-Ion batteries don't like extremes, so going to and staying at low or high SOC is more stress on the battery.

There are a lot of ranges that float around, 30/70, 20/80, 30/60 etc. The difference between them in terms of battery longevity is in my opinion negligible. If you want the battery to last the longest, set it at 50% plugged in and then never drive the car...but then you aren't "grinning"
So, how's your degradation?
 

Baldey

Member
Oct 15, 2019
5
0
Colorado
Thank you guys for the info, this is interesting! I have set my charge limit to 85% (compromise with Elon) , but i'll probably keep dropping it to around 70 as i get used to it (i got a SR+) and charge to 90% on the weekends (i charge for free at the office) .

Would you say it's worth it to trickle charge on my 110v outlet at night on the weekend? I figured i'd just give the batteries a break, and stick to 30A office charging and supercharging if that's ever not enough.. i split the power bill with roommates :p
 

ZOMGVTEK

Member
May 19, 2015
559
442
'Merica
If you can charge moderately consistently at work, I wouldn't worry about trickle charging at home unless its kinda low and you might need it. Regular outlets are SUUUPPER slow.

Probably not much in it dropping the level below ~80% unless the car is parked outside in very hot weather all its life and you don't drive it. Tesla says 90% every day is fine, and that's likely mostly true. Especially in a colder climate, id be very comfortable daily charging to 90%.
 

Baldey

Member
Oct 15, 2019
5
0
Colorado
Sounds good, i'll probably keep charging to 90% or 85% then, and doing the charge to 100% couple times a year thing for calibration. I should be taking at least that many trips :p

I use 20% of the battery (40 miles) to drive 20 miles to work and back. I leave sentry mode enabled at the office, use the AC library, and i am a lead foot.. So i am not super surprised at halving my range lol... but yeah, going from 200 to 160 daily on my SR+ sounds like a plan to me. Thanks again :)
 

camalaio

Active Member
May 28, 2019
1,483
2,181
Vernon, BC, Canada
For the poll, I plug in every day but reach 50% by the time I'm home... so what do I pick? :p

I keep things between 30-80% if I'm "local". If I'm heading out longer distance (<200km round trip) or I know the car will need to sit for a long time in the cold, I'll charge to 90% just before I head out (especially to warm the battery this time of year) but will never plan to drain beyond 10%. I have some range degradation but it's not significant and I'm 15,000km in.

This is surprisingly a common way for people to interpret charge cycles. A charge cycle is considered to be replacing the energy the pack holds from 0-100%. So this means it will take 5 charges from 60-80% to get one full cycle. This is more complex of an issue than you might initially assume, but shallow discharges are quite a bit easier on the battery than deep ones. This doesn't really tell the whole story. The question is how much it matters, and what strain is put on the remainder of the vehicle as a result of more frequent shallow discharges. The car will have more wear elsewhere with being plugged in more frequently. In addition to this, the thermal cycling will accelerate wear on some components. So there is kinda a balance here. You don't really want to plug in to put that 1% back in, but 10-20% is probably sensible if its convenient.

Generally speaking, plugging in every day if you use more than 10% a day is probably 'best'. If you use single digits, maybe every other day. But its really unlikely to be a big deal. I wouldn't worry about it too much. I would expect outright failure of some component is more likely to warrant a pack replacement before degradation hits a level that's considered unacceptable.

For what it's worth, I think many of the more data-driven suggestions regarding charging habits do account for thermal cycling. At Level 2 charging rates, thermal load isn't all that concerning. In cold or winter climates, actively charging is actually helping to keep the battery warmer as well.
 

ZOMGVTEK

Member
May 19, 2015
559
442
'Merica
The best long term storage for lithium tends to be a smidge warmer than whatever temp it takes for the electrolyte to freeze. Higher average temperatures accelerate degradation, how much so depends massively on the chemistry. I was talking more along the lines of the thermal cycling on the charger itself. Power supplies can only be powered up so many times before the weak link fatigues and fails. The problem tends to be differential heating and expansion leading to fatigue failures.

It's hard to say how much of a concern this is at this point. I wouldn't expect this to be an issue for hopefully 10+ years. But more power on cycles WILL accelerate wear on the vehicles internal charger. The question is does the design have enough life to still allow for 20 years of daily cycles. I wouldn't think so, but its possible. Basically its all a trade off between comfort, cell degradation, and the degradation of the rest of the chain. Tesla would be the one to know best here. Unfortunately they aren't always 100% aligned with the best interests of everyone. There's plenty of variables, and I suspect they want a simple approach that works well enough for most. The people that charge to 90% daily and barely drive should still have less degradation than the ones that drive a lot and charge to 90%.
 
Last edited:

camalaio

Active Member
May 28, 2019
1,483
2,181
Vernon, BC, Canada
I was talking more along the lines of the thermal cycling on the charger itself. Power supplies can only be powered up so many times before the weak link fatigues and fails. The problem tends to be differential heating and expansion leading to fatigue failures.

It's hard to say how much of a concern this is at this point. I wouldn't expect this to be an issue for hopefully 10+ years. But more power on cycles WILL accelerate wear on the vehicles internal charger. The question is does the design have enough life to still allow for 20 years of daily cycles. I wouldn't think so, but its possible. Basically its all a trade off between comfort, cell degradation, and the degradation of the rest of the chain. Tesla would be the one to know best here. Unfortunately they aren't always 100% aligned with the best interests of everyone.

Ah, my bad for misreading. Absolutely. I hope Tesla doesn't have electrolytic capacitors anywhere in the charging equipment, and it's quite possible they don't in order to help lifetime and thermal-related wear. But I'm far more OK with replacing the UMC ($370) or a charge port (<$300 I think?) or onboard charger ($???) than a whole battery (over $20,000) down the road.
 

mswlogo

Well-Known Member
Aug 27, 2018
6,152
5,313
MA, NH
A charge cycle implies full charge cycles.

1 at 100% Charge is like 2 at 50% or 4 at 25% or 10 at 10%. Roughly.

So daily is perfectly fine.

What is healthy is keeping track of your average SOC. Shoot for 70% (or even lower).

If you use 40% of battery daily, then charge to 90%. If you only use 20% then charge to 80% etc.

That 40% or 20% of usage doesn't necessary have to span a day. It could be over several days.

I wait until mine drops below 50% and charge to 80%. That might happen in 1 day or 4 days.
 
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