Telsa 80/ 20 or 90/10 rule

[Vladimir*22]

Model X question - My Y will take about 5 - 6 hours to go from 20 - 80% what should i expect for charge times for the X since its a bigger battery?

Tesla general question - If the car sits Sunday - Thursday, I WAH, should it be plugged in Saturday - Wednesday with 50% set and Thursday bring it up to 80% since ill be using it the weekend or let it sit with whatever charge it has all week?

This is interesting - The tech came to my house for another reason, Model Y my X is on order, but anyway this is what he told me:
1. there is a 80/20 or 90/10 rule that Tesla recommends. If you charge to 80% then you dont charge again until its @20%. If you charge to 90% then dont charge again until 10%. Which I think is totally wrong.

2. He said that the degradation comes from charge cycles - his example was if you have 300 cycles until you see degradation then charging every day would start to see it in 1 yr whereas if you charged once a week you would see it in 3 years.

I told him thats not what the manual says and he still stood his ground saying the manual was written before they found this out.

Also, I was told by the same tech that I should change my charging amps to 30/35 instead of the 40/48, I have a 50-amp breaker, because it puts more stress on the breaker which does get warm, the wires, charger and the car. If you are just letting it charge overnight who cares if it takes longer to charge at the lower amps. Thoughts ?????

 

[DCGOO]

Model X question - My Y will take about 5 - 6 hours to go from 20 - 80% what should i expect for charge times for the X since its a bigger battery?

Tesla general question - If the car sits Sunday - Thursday, I WAH, should it be plugged in Saturday - Wednesday with 50% set and Thursday bring it up to 80% since ill be using it the weekend or let it sit with whatever charge it has all week?

This is interesting - The tech came to my house for another reason, Model Y my X is on order, but anyway this is what he told me:
1. there is a 80/20 or 90/10 rule that Tesla recommends. If you charge to 80% then you dont charge again until its @20%. If you charge to 90% then dont charge again until 10%. Which I think is totally wrong.

2. He said that the degradation comes from charge cycles - his example was if you have 300 cycles until you see degradation then charging every day would start to see it in 1 yr whereas if you charged once a week you would see it in 3 years.

I told him thats not what the manual says and he still stood his ground saying the manual was written before they found this out.

Also, I was told by the same tech that I should change my charging amps to 30/35 instead of the 40/48, I have a 50-amp breaker, because it puts more stress on the breaker which does get warm, the wires, charger and the car. If you are just letting it charge overnight who cares if it takes longer to charge at the lower amps. Thoughts ?????

#1 completely wrong.
I charge every night to 75%, regardless of how little energy is consumed. If I have an extended trip, I might charge to 90 or 95 overnight, then top off to 100 before departing. It is simply wrong, to not charge because you didn't drive much. If you charge from 70% to 80% that is roughly one eighth of a cycle.

#2 Also wrong.
Degradation mostly comes from calendar aging, assuming rational behavior getting there.

#3 If you have a 50 amp breaker, you will be limited to the capacity of the charging connector or 40 amps. If you have a hardwired wall connector, you could charge up to 48 amps, but that requires a 60 amp breaker and adequate wiring (that is what I am doing). There is no need to reduce the charge rate. Circuit breakers are SUPPOSED to get warm at 80% of rated. If they did not get warm, they would not ever trip.

 

[henderrj]

#1 completely wrong.
I charge every night to 75%, regardless of how little energy is consumed. If I have an extended trip, I might charge to 90 or 95 overnight, then top off to 100 before departing. It is simply wrong, to not charge because you didn't drive much. If you charge from 70% to 80% that is roughly one eighth of a cycle.

#2 Also wrong.
Degradation mostly comes from calendar aging, assuming rational behavior getting there.

#3 If you have a 50 amp breaker, you will be limited to the capacity of the charging connector or 40 amps. If you have a hardwired wall connector, you could charge up to 48 amps, but that requires a 60 amp breaker and adequate wiring (that is what I am doing). There is no need to reduce the charge rate. Circuit breakers are SUPPOSED to get warm at 80% of rated. If they did not get warm, they would not ever trip.

Absolutely agree, as to the battery issues. Although I would agree degradation by age is a significant issue, usage does have a notable effect. And we are learning a lot still. batteries that are apparently identical often have double or even tripled the amount of age and/or usage before failure.

I would think that high C rate charging (i.e. above 150 kilowatt, depending on size and chemistry) may be the greatest cause of degradation. Although leaving these NMC batteries at a high state of charge has shown increased dendrite development, which causes significantly increased degradation rates. So maybe that's worse yet. I think the basic instruction of keeping your battery between 80 and 20%, except for short periods of time is probably the best advice if you're trying for longevity of the battery.

It's sad how many Tesla Representatives have no idea what they're talking about but say it was such a great authority! I've been following lithium ion battery work for a few decades now, even have a patent on charging, this is just flat out wrong. Unfortunately he seems to have confused charging sessions with charging cycles.

 

[E90alex]

Tesla general question - If the car sits Sunday - Thursday, I WAH, should it be plugged in Saturday - Wednesday with 50% set and Thursday bring it up to 80% since ill be using it the weekend or let it sit with whatever charge it has all week?

It would be better for the battery to sit at 50% or less. If you truly don’t need to use the car the rest of the week then you can even leave it unplugged after your weekend use and just plug it in Thursday night and have it set to finish charging by whenever you need it Friday.

Are you leaving town on the weekends that you need 80% charge? If you’re just running errands locally then most likely even 50% would be enough daily charge on the weekends.

 

[mxnym]

I'm only chiming in to point out that Tesla does revise the manual (for instance, this particular legacy manual page would have been drastically different in 2015-2018 before v10 was released). Considering that this particular tech apparently didn't even know that, one should rest assured that said tech was more concerned with saving face than facts. It may be possible that the tech actually misinterpreted things similar to those stated here, but I not aware of any official documentation that says anything about 80% or 20%, so I find that unlikely.

 

[Vladimir*22]

It would be better for the battery to sit at 50% or less. If you truly don’t need to use the car the rest of the week then you can even leave it unplugged after your weekend use and just plug it in Thursday night and have it set to finish charging by whenever you need it Friday.

Are you leaving town on the weekends that you need 80% charge? If you’re just running errands locally then most likely even 50% would be enough daily charge on the weekends.

I normally just hang out around town - I use around 50% of battery from Friday - Sunday so I usually charge it on Thursdays to 80% and let it sit the rest of the week unless I need a quick trip to store. Usually i am 35-40% of charge left by Thursday. So I guess the best would be charge to 50% and just charge up every time I get home which is fine because its in the garage with the charger.

I want to keep my X, once I get it for 5-7 years, so definitely want a better understanding of the battery charging. I have 5500 miles on my Y and not getting a true 80-90% numbers, but I also think the 330 rated is not real-world numbers.

 

[E90alex]

Yes the Tesla rated range number are basically not achievable in the real world conditions. Knock 10-15% off those numbers at the minimum.

 

[TacoGuy]

#3 If you have a 50 amp breaker, you will be limited to the capacity of the charging connector or 40 amps. If you have a hardwired wall connector, you could charge up to 48 amps, but that requires a 60 amp breaker and adequate wiring (that is what I am doing). There is no need to reduce the charge rate. Circuit breakers are SUPPOSED to get warm at 80% of rated. If they did not get warm, they would not ever trip.

OP - following this, you need 60A breaker to charge @ 48A. Make sure the breaker has the correct Amp load rating and C rating. Breakers trip due to excess heat, which is the primary identifier of a short. Shorted current should go to ground if wired properly and not cause an issue in the time it takes until the breaker pops.

 

[Vladimir*22]

OP - following this, you need 60A breaker to charge @ 48A. Make sure the breaker has the correct Amp load rating and C rating. Breakers trip due to excess heat, which is the primary identifier of a short. Shorted current should go to ground if wired properly and not cause an issue in the time it takes until the breaker pops.

Thank you - I am only doing 40 Amps what I meant was what I see on the screen was 40 of the max 48amps

 

[Vladimir*22]

Yes the Tesla rated range number are basically not achievable in the real world conditions. Knock 10-15% off those numbers at the minimum.

You hit those numbers perfectly - with a 90% charge I am at 84% of the tesla fake numbers 280 vs 330 range.

 

[TacoGuy]

You hit those numbers perfectly - with a 90% charge I am at 84% of the tesla fake numbers 280 vs 330 range.

In 3 months lifetime is 270W/Mi assuming 75kwh usable battery in MYLR, that's 278Mi. More reasonable/expected.

 

[TacoGuy]

Absolutely agree, as to the battery issues. Although I would agree degradation by age is a significant issue, usage does have a notable effect. And we are learning a lot still. batteries that are apparently identical often have double or even tripled the amount of age and/or usage before failure.

I would think that high C rate charging (i.e. above 150 kilowatt, depending on size and chemistry) may be the greatest cause of degradation. Although leaving these NMC batteries at a high state of charge has shown increased dendrite development, which causes significantly increased degradation rates. So maybe that's worse yet. I think the basic instruction of keeping your battery between 80 and 20%, except for short periods of time is probably the best advice if you're trying for longevity of the battery.

It's sad how many Tesla Representatives have no idea what they're talking about but say it was such a great authority! I've been following lithium ion battery work for a few decades now, even have a patent on charging, this is just flat out wrong. Unfortunately he seems to have confused charging sessions with charging cycles.

Charging at high rates, and hard discharging will generate heat. My understanding is that the heat cycles produce crystalline structures in the electrolytic substrate within the battery. The crystalline structures raise overall internal resistance as well as creating shunts to prevent electron exchange from cathode to anode resulting in reduced capacity (lower total discharge current) over time. Additionally, there are negative affects to having a battery sitting at low SoC, that could affect the lifespan of the battery.

While I don't have the science, I think the best thing to watch out for is heat. Whether the heat comes from Charge/Discharge, or the whole cycle, heat causes more deg than the normal cadence of charging and discharging. You can avoid heat by keeping pack within operating range(Tesla does this with active cooling), not pushing charging rate to max every charge (Limited use of super-chargers), and managing duty cycle of the vehicle (Operating in chill mode, not smashing the accelerator at every green light, and keeping the consumption of power at a reasonable rate within rated range W/Mi)

 

[DCGOO]

It would be better for the battery to sit at 50% or less. If you truly don’t need to use the car the rest of the week then you can even leave it unplugged after your weekend use and just plug it in Thursday night and have it set to finish charging by whenever you need it Friday.

Are you leaving town on the weekends that you need 80% charge? If you’re just running errands locally then most likely even 50% would be enough daily charge on the weekends.

I slightly disagree here. It is true you *could* leave it unplugged and have no issue. But if it is easy for you to plug it in, such as at home in your own garage, you might as well leave it plugged in. It will stop charging when it gets to your chosen amount, and keep it there by coming on for a short time every few days.

 

[henderrj]

Being careful with your battery is of course important. However, do have fun with the car! That is why we buy them after all. If we use up the car, That's not such a bad thing is it? Hopefully we use it up about the same time that we want a new one!

 

[Rocky_H]

2. He said that the degradation comes from charge cycles - his example was if you have 300 cycles until you see degradation then charging every day would start to see it in 1 yr whereas if you charged once a week you would see it in 3 years.

This is utter nonsense. He is misunderstanding that a charging event IS NOT the same thing as a charging cycle. A cycle is equal to draining and refilling the amount of the full capacity of the battery. If you drain and refill 50% once, that is half a cycle. If you drain and refill 10% five times, that is also half a cycle. So he's totally wrong on that 1 year versus 3 years thing. Cycles runs basically proportional to your total miles, since it's just about energy consumed and refilled.

1. there is a 80/20 or 90/10 rule that Tesla recommends. If you charge to 80% then you dont charge again until its @20%. If you charge to 90% then dont charge again until 10%. Which I think is totally wrong.

This one has an interesting mix to it, because there are two different factors going in opposite directions:
1. Shallow drain and refill events are healthier for a battery than deep discharge and big refill events. The car manual even says there is no benefit in intentionally running it down low first. So he is mostly wrong here.
2. But for most of the time-based calendar aging, sitting at lower states of charge is healthier than at higher states of charge. So gradually running it down has an unintentional side effect of having it sit around that 40-50% kind of levels more than always being up around 70-80%. So there would be some slight benefit there. I think these are mostly imperceptible differences you won't notice much in the first 10 or 20 years of the battery's life, though.

Also, I was told by the same tech that I should change my charging amps to 30/35 instead of the 40/48, I have a 50-amp breaker, because it puts more stress on the breaker which does get warm, the wires, charger and the car. If you are just letting it charge overnight who cares if it takes longer to charge at the lower amps. Thoughts ?????

This one is kind of interesting too. It's not really for the car's sake. But for extending the life of your charging cables and equipment, yes, it can be beneficial to use them a bit below their maximum rated level to not warm them up as much. Electronics and solder connections and stuff is stressed by thermal cycling. Metals expand and contract as they heat and cool with each daily use. Having that daily temperature swing be smaller can be easier on that equipment long term.