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Another charging battery life thread

Zoomit

Active Member
Sep 1, 2015
2,302
4,530
SoCal
Is Depth of Charge more important or State of Charge more important?

If I charge to 75% and drive to 50%, should I recharge back to 75%? (Less Depth of Charge)

Or should I wait until 25% to recharge? (Less State of Charge)
No simple answer is possible. It depends. For example, high SoC degradation is temperature dependent but depth of discharge is not (to my knowledge). So in a hot storage environment you might favor the lower SoC over the higher DoD.
 
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Hiline

Member
Supporting Member
Apr 16, 2022
635
884
Los Angeles
No simple answer is possible. It depends. For example, high SoC degradation is temperature dependent but depth of discharge is not (to my knowledge). So in a hot storage environment you might favor the lower SoC over the higher DoD.
How impactful is storage environment? I thought the BMS was supposed to regulate the temperature of the battery.
 
This is very interesting, I have a question i tried to google with no definitive answer. I read keeping the battery arouund 50pc to keep the battery balanced between anode and cathode and have less stress, like a rubber band, is best. My question is what speed to charge at when plugged in at home. I can use the app to charge at a minimum 5 amps then 12, 24, 36 or a max of 48 amps. Should I charge at the slowest rate to not overheat the battery? Charging at 48 amps makes the breaker panel hot. Usually I charge at 12 amps.

What do you think is the best charge speed for at home charging?
 
This is very interesting, I have a question i tried to google with no definitive answer. I read keeping the battery arouund 50pc to keep the battery balanced between anode and cathode and have less stress, like a rubber band, is best. My question is what speed to charge at when plugged in at home. I can use the app to charge at a minimum 5 amps then 12, 24, 36 or a max of 48 amps. Should I charge at the slowest rate to not overheat the battery? Charging at 48 amps makes the breaker panel hot. Usually I charge at 12 amps.

What do you think is the best charge speed for at home charging?
I don’t think anyone can say without actual
Information on the temperature of the battery. I wouldn’t worry too much about battery temperature - the computer will cool and adjust the battery as necessary and the ambient rest temperature of the battery probably plays a much larger roll than the temp when charging just by virtue of the total time spent charging vs at rest.

What I would be worried about is the breaker panel getting hot. I’d suggest having that checked by an electrician.
 
Tesla does, indeed, regulate pack temperature. But not efficiently. And it makes no pretense about maintaining pack temperature at a level that is optimum (~20-25C) for pack longevity.

My observations from frequent monitoring of actual pack temps, in a 2022 Model 3, during summer in the Mid-Atlantic, with the vehicle parked in outdoor conditions...

  • The pack readily absorbs heat from high ambient temps, even when parked in the shade
  • Running AC (climate on) does not meaningfully affect pack temperature.
  • The pack very quickly absorbs heat when parked in direct sunlight. Enabling Cabin Overheat Protection has little-to-no affect on this; nor does running cabin AC
  • Airflow (such as when driving) has negligible affect on pack cooling
  • Once the pack has reached a moderately elevated temp (e.g. ~35-40C), it cools very slowly (over many hours); lagging actual ambient temp decline (such as overnight)
All studies of both calendar and cyclic aging of Lithium-ion battery chemistries strongly correlate elevated pack temperatures with accelerated pack degradation. Alas, pack temperature is difficult for most users to meaningfully manage. And Tesla's BMS is far from the efficient, optimum piece of engineering it is often touted to be, with respect to that cooling. I'm not at all suggesting that that - optimum pack thermal management - is an easy thing to achieve. To the contrary, the fact that it isn't is no doubt the way things are the way they are.

But it does emphasize the need for owners to be mindful of those things that they can influence... SOC and depth of discharge.
 
There are a lot of LFP batteries out there now. We have a 2021 SRP LFP and a 2022 LR...
How do you treat/charge these differently? Other than the obvious that you charge an LFP to 100% or because of that does none of this apply?

Thx.
 
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Boza

2020 Model S LR+
Sep 24, 2021
853
1,379
Usa
You guys are worrying too much. I charge my Raven S to 90% routinely . At 38000 miles it’s down 13 miles from new. I live in a hot climate that is supposed to be harder on lithium ion batteries. Frankly, based on trips I make routinely, I’m not sure it’s lost even that much.
What is your ambient temperature? What is the actual battery capacity? There are a few treads discussing range estimation and after reading them I decided to use actual capacity as baseline (although it still uses the range estimator). I use SOC rather than miles in my IC anyway.

I have 2020 Raven SLR+ and never charged more than 90%. On a few occasions I used SC and on a few occasions I went down below 20% (still never single digit).

Most common use case is going down to ~50% during the daily drive and then L2 (32A) charge overnight to 60%. Essentially, daily 10kWh top up.

One of garages is warm - regularly 28-29’C. I noticed more overnight power loss in it and I attribute it to the BMS cooling the battery but it may be faster discharge due to higher pack temperature. It is not much - less than one kWh per 24hrs - but noticeably more than the other, cooler place.

Depending on when I measure it, the battery is between 95kWh and 98kWh. Interestingly, it is closer to 95kWh at the extremes - around 25% and 90%. That would be between 2% and 5% degradation for 2yrs/34k miles - assuming the usable part of the battery is 100kWh and the rest is reserve.

I also did some research about the optimum L2 charging current. While true that 48A is nothing compared to SC, it still likely turn the BMS cooling on. On the other hand, trickle charge will keep the car awake for longer. That has an effect on the range calibration (the car must be asleep for a few hours for this to kick in) and may have negative effect on the flash. Even though Ravens have upgraded flash, it still has a limit and appears that the car writes to it while awake. I found that 24A - 32A is the happy optimum where I get the fastest charge without BMS kicking it. It is definitely ambient temperature dependent.

It also seems that the range estimator needs the car to be asleep at different SOC levels in order to improve accuracy. Given my practice, my estimator may be off; hence the difference in capacity numbers between different SOC.

In the past few months, starting probably with 2022.4, I noticed that the charger “overshoots” quite often at the higher SOC. When I ask for 90% and start from 30%-40% it will stop charging at 91%-92% instead of 90%.

I know that I may be “pixel peeping” but I am interested in this as a physics/engineering problem. Completely aware that in the grand scheme of things the difference may be negligible. Many people will drive according to their habits and would not care.
 
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Boza

2020 Model S LR+
Sep 24, 2021
853
1,379
Usa
Too low SOC for LiPo will damage the cathode. The result is increased internal resistance of the battery. While BMS has a minimum threshold to prevent immediate permanent damage, it is a gradual risk and it is good to have a buffer. There is evidence that regularly deep discharged batteries have shorter life.

Based on the information in this and other treads the best SOC is ~50%-60%. BTW, LiPo batteries are stored/shipped at ~60% SOC.
 
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...

One of garages is warm - regularly 28-29’C. I noticed more overnight power loss in it and I attribute it to the BMS cooling the battery but it may be faster discharge due to higher pack temperature. It is not much - less than one kWh per 24hrs - but noticeably more than the other, cooler place.

...

I also did some research about the optimum L2 charging current. While true that 48A is nothing compared to SC, it still likely turn the BMS cooling on.

Have you taken actual pack temp measurements? I've seen scant evidence that the BMS is actively cooling the pack at the temps likely generated with L2 charging.

What I'll observe - on the Model 3 pack, at least - is that during the summer pack temps rise rapidly when the car is driven; and when it is parked in direct sunlight. It typically stabilizes at ~35-40C (95-105F).

Air cooling of the pack (via driving) is negligible.

And the pack will retain those elevated temps for many hours, only very slowly declining as ambient temps slowly come down (such as overnight).

I have not observed any evidence of active pack cooling at those ~35-40C temps. And my (20-amp) L2 charger does not seem to add any noticeable heat. I'd be surprised to hear that higher-amperage L2 charging generates meaningfully higher temps; or that active cooling by the BMS is triggered.

Happy to learn something new, if that, indeed, is the case.
 

Boza

2020 Model S LR+
Sep 24, 2021
853
1,379
Usa
Have you taken actual pack temp measurements? I've seen scant evidence that the BMS is actively cooling the pack at the temps likely generated with L2 charging.

What I'll observe - on the Model 3 pack, at least - is that during the summer pack temps rise rapidly when the car is driven; and when it is parked in direct sunlight. It typically stabilizes at ~35-40C (95-105F).

Air cooling of the pack (via driving) is negligible.

And the pack will retain those elevated temps for many hours, only very slowly declining as ambient temps slowly come down (such as overnight).

I have not observed any evidence of active pack cooling at those ~35-40C temps. And my (20-amp) L2 charger does not seem to add any noticeable heat. I'd be surprised to hear that higher-amperage L2 charging generates meaningfully higher temps; or that active cooling by the BMS is triggered.

Happy to learn something new, if that, indeed, is the case.
Good point about the actual temperature. I will start tracking that.

In a 29’C garage with 48A L2 the BMS is definitely turning on the cooling during charging. I can hear it about 10 min after the charging starts.
 
Have you taken actual pack temp measurements? I've seen scant evidence that the BMS is actively cooling the pack at the temps likely generated with L2 charging.

What I'll observe - on the Model 3 pack, at least - is that during the summer pack temps rise rapidly when the car is driven; and when it is parked in direct sunlight. It typically stabilizes at ~35-40C (95-105F).

Air cooling of the pack (via driving) is negligible.

And the pack will retain those elevated temps for many hours, only very slowly declining as ambient temps slowly come down (such as overnight).

I have not observed any evidence of active pack cooling at those ~35-40C temps. And my (20-amp) L2 charger does not seem to add any noticeable heat. I'd be surprised to hear that higher-amperage L2 charging generates meaningfully higher temps; or that active cooling by the BMS is triggered.

Happy to learn something new, if that, indeed, is the case.
You're correct that you have to look at the actual battery temperature. I believe Scan My Tesla will give you the information but there are probably other ways.

@Regaj - I'd note that your experience is not necessarily incompatible with @Boza's. You're only charging at 20A so that may not be enough current to appreciably heat up the battery and trigger active cooling.
 
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Boza

2020 Model S LR+
Sep 24, 2021
853
1,379
Usa
Using TesLax and ScanMyTesla I noticed some interesting data:
- Ambient temperature 20’C; pack temperature 29’C (after driving 20mi). It takes a long time to passively cool off the pack. The active cooling kicks above 40’C. Air cooling while driving does not have meaningful effect
- The car was passively cooling until it went to sleep. Then it fired the active cooling for about 30sec and then it turned it off. I guess it was part of going to sleep.
- There is some discrepancy between what the car shows as W/mi and projected range and what the apps show. Both apps show lower consumption and range. SMT shows 5kWh reserve on the battery - that may have something to do with it.
I was surprised how warm the pack was despite the ambient temperature.
 
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Using TesLax and ScanMyTesla I noticed some interesting data:
- Ambient temperature 20’C; pack temperature 29’C (after driving 20mi). It takes a long time to passively cool off the pack. The active cooling kicks above 40’C. Air cooling while driving does not have meaningful effect
- The car was passively cooling until it went to sleep. Then it fired the active cooling for about 30sec and then it turned it off. I guess it was part of going to sleep.
- There is some discrepancy between what the car shows as W/mi and projected range and what the apps show. Both apps show lower consumption and range. SMT shows 5kWh reserve on the battery - that may have something to do with it.
I was surprised how warm the pack was despite the ambient temperature.
Not terribly surprising that the ambient temp doesn’t affect it much - air flows under the car but there’s a plastic plate plate that protects the battery and also serves as an insulator. Regardless the majority of the battery’s not exposed so it’s not a very good design for Passive cooling. THe battery also has a large thermal mass so it will be slow to cool anyway.
 

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