How to charge at home?

[Diehard]

Which one is worse for the battery; higher number of cycles? Or spending more time at SOCs away from from 50%? Assuming in both cases you consume the same number of KWhs annually. In other words charging to 90% using 10% every day until you hit 10% (1 cycle but spending a day at 90% and a day at 10%) vs going from 60% to 40% (4 cycles but spending 4 days at 50% ).

Also, I have heard when you drive home, you should let the truck sit for a few hours for the battery to balance before you charge. I also heard battery does not like to be at low SOC and like to charged at temps closer to body temperature. So if I get home at 10% SOC when temp outside is 35 degrees and battery is warm from driving, which one takes precedence? Is it better to charge immediately or wait a few hours to charge?

How significant is the difference?

If you have source for your answers please share. If you don’t, I still like to read your opinion with your reasoning.


p.s. everyone has been posting on YouTube about a model 3 battery that died after 120K. Apparently there were a lot of DCFC charging involved but recently Tesla data indicated DCFC charging is not that big of a deal. Although this video did trigger my question, it is just a background info not the actual topic. I still would like to have the answers independent of this incident.

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[CyberGus]

Which one is worse for the battery; higher number of cycles? Or spending more time at SOCs away from from 50%? Assuming in both cases you consume the same number of KWhs annually. In other words charging to 90% using 10% every day until you hit 10% (1 cycle but spending a day at 90% and a day at 10%) vs going from 60% to 40% (4 cycles but spending 4 days at 50% ).

Also, I have heard when you drive home, you should let the truck sit for a few hours for the battery to balance before you charge. I also heard battery does not like to be at low SOC and like to charged at temps closer to body temperature. So if I get home at 10% SOC when temp outside is 35 degrees and battery is warm from driving, which one takes precedence? Is it better to charge immediately or wait a few hours to charge?

How significant is the difference?

If you have source for your answers please share. If you don’t, I still like to read your opinion with your reasoning.


p.s. everyone has been posting on YouTube about a model 3 battery that died after 120K. Apparently there were a lot of DCFC charging involved but recently Tesla data indicated DCFC charging is not that big of a deal. Although this video did trigger my question, it is just a background info not the actual topic. I still would like to have the answers independent of this incident.

"One cycle" is the consumption of the entire pack capacity (100% to 0%). If you charge to 80% and drive it to 30%, that is only 1/2 cycle. (Lithium cells have no "memory", they're not NiCads lol)

Cells degrade with age, and this accelerates with SoC over 50% and greatly over 90%. Store at 50%, and plan your charge sessions to hit "full" just before you depart.

The battery pack will be heated (or cooled!) for charging. Charging will be slower at low ambient temps because it needs more power to warm the battery.

The cells will self-balance. The issue with "letting it sit" is that the BMS uses idle periods to calibrate, so you should periodically let it sleep for a few hours without any charging so that your range estimates will be more accurate.

You can drive your pack all the way to 0% without harm, since that is NOT "zero volts". If you leave it in this state however, it will slowly self-discharge until it does hit zero volts, at which point you'll be buying a new pack.

Degradation does not cause your pack to "fail", it reduces capacity and range. Pack failures are the result of one or more individual cells failing, impairing the whole string of cells. This should be rare, and is difficult to predict.

 

[Diehard]

Cells degrade with age, and this accelerates with SoC over 50% and greatly over 90%. Store at 50%, and plan your charge sessions to hit "full" just before you depart.

You can drive your pack all the way to 0% without harm, since that is NOT "zero volts".

are you saying sitting at 45% over 50% (95% SOC) for 24 hours is worse than 45% under 50% (5% SOC) for a day (provided there is only 1% daily loss)?

 

[CyberGus]

are you saying sitting at 45% over 50% (95% SOC) for 24 hours is worse than 45% under 50% (5% SOC) for a day (provided there is only 1% daily loss)?

Well...it's complicated

There's a curve of "degradation vs. SoC" but it will vary the cell chemistry, temperature, etc. Broadly speaking, the worst-case scenario is to charge to +90% and leave it there.

 

[CyberGus]

If you want the full lowdown, ingest this TMC thread:

https://teslamotorsclub.com/tmc/thr...iciency-how-to-maintain-battery-health.166549

It's only 300 pages over 4 years lol

 

[Crissa]

All this varies by chemistry, which we won't know the specifics, other than 'high nickel'. And how the battery does cell balancing... I don't know how a Tesla does it, but there are many different schemes. This one seems to indicate Tesla uses two schemes; a 100% charge scheme (where it balances when it's at 100%) and a settling scheme (where it wants to sit at ~60% and see which cells rebound without significant draw):

https://tesla-info.com/guide/tesla-bms-calibration.php

The battery can charge faster when it's warmer. But AC charging is super slow, compared to the battery size, and so doesn't really need that optimal temperature. The electrons have time to find their ions at the cooler temps.

From those charts, there's not a huge amount of difference between staying between 20%-80% and staying between 40%-60% over times if you calculate for energy use.

And the penalty for short term excursions to 100% or 0% are almost statistically unnoticeable.

A Tesla can be told to use shore power not to charge but only for essential functions - like warming the pack, communications, etc - and to charge within specific hours.

So really, a battery benefits from both hanging out near that 50% and by going to 100% and down into the low % to see how it's doing.

-Crissa

 

[Diehard]

Thanks everyone. Lots of great info here. The links are very helpful as well.

 

[CyberJagg]

Which one is worse for the battery; higher number of cycles? Or spending more time at SOCs away from from 50%? Assuming in both cases you consume the same number of KWhs annually. In other words charging to 90% using 10% every day until you hit 10% (1 cycle but spending a day at 90% and a day at 10%) vs going from 60% to 40% (4 cycles but spending 4 days at 50% ).

Also, I have heard when you drive home, you should let the truck sit for a few hours for the battery to balance before you charge. I also heard battery does not like to be at low SOC and like to charged at temps closer to body temperature. So if I get home at 10% SOC when temp outside is 35 degrees and battery is warm from driving, which one takes precedence? Is it better to charge immediately or wait a few hours to charge?

How significant is the difference?

If you have source for your answers please share. If you don’t, I still like to read your opinion with your reasoning.


p.s. everyone has been posting on YouTube about a model 3 battery that died after 120K. Apparently there were a lot of DCFC charging involved but recently Tesla data indicated DCFC charging is not that big of a deal. Although this video did trigger my question, it is just a background info not the actual topic. I still would like to have the answers independent of this incident.

I think it’s best to wait until we have the truck and play around with it for the first week or 2 to know what works best for each use case!

 

[Diehard]

I think it’s best to wait until we have the truck and play around with it for the first week or 2 to know what works best for each use case!

You know we are no good when it comes to waiting around here. Especially to answer my questions, we may have to play around with CT for a decade or two. Unless we get a Solid State 4680 in CT. Now, that would make the announcement at the end of the month something of a historic moment.

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