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I drive 5-8% of the battery per day. WHICH 5-8% should I use?

I have a short commute. The car is plugged in every night to charge. Given the low daily consumption, what is the best 5-8% of the battery to use for its health? 60-52? 50-42? Higher or lower? Current daily charge level is 60%, which is based on research on this forum and a couple other places.
 
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Saghost

Well-Known Member
Oct 9, 2013
8,224
7,098
Delaware
There are two logical choices, with different logic for each.

The least wearing cycle would be something like 46-54% (though below 80% the difference is minimal.)

The downside to that is from about 20% to about 80% the voltage is constant, so the only way the car knows how much charge is in the battery is a math model based on power flows in and out - and those models can get confused or drift over time.

Which leads to the other logical choice - charge to 90% and don’t worry about it.

That’s Tesla’s official recommendation these days, and I’m pretty sure they recommend that because it gives the math models something to work with - the cell voltage is slightly above the constant range, in an area where voltage corresponds quite consistently with state of charge, and the wear on the pack is only slightly greater.

I use around ten percent per day and take a lot of longer trips that aren’t really planned, so I picked something in the middle. I charge to 80% on a daily basis, and to 90% on trips and if the 80% number moves much (and I have seen it change by several miles and come back when I charge to 90%.)
 
The downside to that is from about 20% to about 80% the voltage is constant, so the only way the car knows how much charge is in the battery is a math model based on power flows in and out - and those models can get confused or drift over time.
It isn't constant but it does not change much with respect to SoC so that augmentation by coulomb counting is necessary and even then an occasional "calibration" by visiting the high and low SoC regions is needed.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
8,582
11,136
Boise, ID
In the belief that it is the number of charge/discharge cycles that ultimately determine battery life I let it get down to around 40% and then charge it back up to about 75%.
That is not changing the number of cycles. A cycle is defined as the full capacity of the battery, regardless of how many sessions you break that up into.
 

Eno Deb

Active Member
Aug 17, 2018
2,641
3,402
SF Bay Area
I have a short commute. The car is plugged in every night to charge. Given the low daily consumption, what is the best 5-8% of the battery to use for its health? 60-52? 50-42? Higher or lower? Current daily charge level is 60%, which is based on research on this forum and a couple other places.
What you're currently doing is pretty much optimal. Don't overthink it. ;) Personally I also have a rather short commute and usually charge to 70%, but right now I've set it a bit higher because we've had some power outages related to the California fires.
 
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nwdiver

Well-Known Member
Feb 17, 2013
9,131
13,847
United States
In the belief that it is the number of charge/discharge cycles that ultimately determine battery life I let it get down to around 40% and then charge it back up to about 75%.

A 35% cycle causes significantly more degradation than 7 5% cycles. Smaller cycles reduce degradation.

Depth-of-discharge-versus-cycle-life-of-the-lithium-ion-battery.png
 

mtndrew1

Active Member
May 12, 2015
1,501
4,410
Gardena, CA
A 35% cycle causes significantly more degradation than 7 5% cycles. Smaller cycles reduce degradation.

Depth-of-discharge-versus-cycle-life-of-the-lithium-ion-battery.png

I’m under the impression that one cycle is a complete 100%-0%.

For example, five 20% discharge/recharge events would be one cycle.

That said, I typically charge to 80% since I use about 10% per day. Lithium batteries are happiest avoiding the extremes.
 
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nwdiver

Well-Known Member
Feb 17, 2013
9,131
13,847
United States
I’m under the impression that one cycle is a complete 100%-0%.

For example, five 20% discharge/recharge events would be one cycle.

That said, I typically charge to 80% since I use about 10% per day. Lithium batteries are happiest avoiding the extremes.

Yes; (5) 20% discharge/recharge events would be one cycle.... which is why I was using (1) 35% vs (7) 5%... smaller cycles are key to a long lived battery. Avoiding the extremes is important too.
 
A 35% cycle causes significantly more degradation than 7 5% cycles. Smaller cycles reduce degradation.

Depth-of-discharge-versus-cycle-life-of-the-lithium-ion-battery.png
This is a little apples and oranges to this discussion as the x-axis is DoD.

So in other words this chart says that if you go from 100% to 50%, every time, then a typical Li-Ion batt would last 10,000 cycles (which would be 20,000 charges from 50% to 100%).

This chart says absolutely nothing about what it means for cycle life if you go from, say, 75% to 25% as it DoD charts always assume starting 100% SOC (state of charge).
 

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