What should my ideal charge percentage be?

[arnis]

December 2016

1 summer is absolutely nothing in terms of meaningful data. Reported range is not science,
it's estimation that varies at least 1-2% depending on circumstances.

One day per week at 80% is very good. But charging once a week in not optimal.
Actually, using 260 mile range vehicle for 24 miles per day in not optimal, but that is another story.

 

[gavine]

Li-ion battery doesn't care how often you charge it. It only cares how high is the state of charge for how long and how hot.
Keeping state of charge between 30%-50% is extremely ideal for normal and warm climates.

It also cares about depth of discharge so shallow cycles are better than deep cycles.

 

[whttiger25]

There is lots of good advice here. Much of the more detailed and rigorous advice will very marginally help your battery over the very long term. To keep things simple, I would say:

- Charge to 100% when you need it, and when you are ready to use it
- Daily charge to 70-80%.
- Store at 50%
- Plug in whenever you can.

And here is the MOST important one to add:
- Change battery indicator from range miles to percentage. This will prevent you from suffering from "range loss anxiety", the natural successor to "range anxiety" for those of us that simply have to be anxious about something.

 

[arnis]

It also cares about depth of discharge so shallow cycles are better than deep cycles.

Actually it cares about "height" of charge, not depth of discharge. It's almost the same thing, but not exactly.
I discharge my EV pack "too much too often" (way below 3V per cell) and it has one of the best health over 4 years in my region.
I estimate at least 200 cycles below 3V and at least 50 cycles below 2.8V. This is very very very low end. And pack is SUPER happy.
Depth of discharge doesn't matter. But charging "height" does. Damage is done at higher voltage, no damage at low end.
There are things that start to happen below 2.5V, but this is not reachable anyway.

 

[Olds442]

\
And here is the MOST important one to add:
- Change battery indicator from range miles to percentage. This will prevent you from suffering from "range loss anxiety", the natural successor to "range anxiety" for those of us that simply have to be anxious about something.

this is great advise. i changed it shortly after the first time i saw it posted. what i find funny is i was always one of those people that ran my tank down to well past "E", and past when the warning light says 30 miles remaining, to the point where it says unknown miles remaining. only then would i stop to fill 'er up.

i typically charge to 80, but sometimes 90 if i have a lot of running around to do. when i go out of town and leave it at home i'll set it to 50 or 60 based on what people have posted here. i always plug it in at home and leave it that way until heading out.

i only feel range anxiety on road trips, day to day isn't an issue.

 

[gavine]

Actually it cares about "height" of charge, not depth of discharge. It's almost the same thing, but not exactly.
I discharge my EV pack "too much too often" (way below 3V per cell) and it has one of the best health over 4 years in my region.
I estimate at least 200 cycles below 3V and at least 50 cycles below 2.8V. This is very very very low end. And pack is SUPER happy.
Depth of discharge doesn't matter. But charging "height" does. Damage is done at higher voltage, no damage at low end.
There are things that start to happen below 2.5V, but this is not reachable anyway.

I wasn't aware of that. I always thought going, let's say from 80 to 50% daily is better than going from 80 to 20% daily. Not because 20% is bad, but because it's a deeper cycle. I learned this here:

Is it okay to only fast charge?

"The other issue is the depth of discharge (difference between highest and lowest SOC). For longer life, it is best to minimize this range. You can think of bending a piece of metal. Bending the metal 360 degrees once (so it is folded in half and then folded in half in the other direction) is more stressful than bending it 180 degrees twice. Similarly, discharging all the way to 0% and charging all the way to 100% is more stressful because there is a larger range of expansion and contraction of the battery material, which degrades it more quickly (cracks are formed more easily)."

 

[juju]

Guy at the Tesla store told me former VP of Engineering recommended charging to 80%. I bought my Model S used and the daily charge limit was already set to 80. Haven't changed it since.

 

[arnis]

I wasn't aware of that. I always thought going, let's say from 80 to 50% daily is better than going from 80 to 20% daily. Not because 20% is bad, but because it's a deeper cycle. I learned this here:

Well 80 down to 50 will result in less mileage than 80 down to 20. Driving less is not an option if we measure degradation over
time (one year) and/or mileage (20 000 miles).
What is an option in that case is:
drive 80 down to 50 and charge back to 80 (daily charging) or
drive 80 down to 50. Don't charge. Next day drive 50 down to 20. Charge to 80 (charging every second day).

If we compare these two, then charging every second day is better for battery as average state of charge will be lower
(every second night battery is kept at 50%, which is ever so slightly healthier than 80%).

And charging daily from 20 to 50 is even better than from 20 to 80 every second night.
In conclusion, depth is not important

 

[Texas]

I have kept my charge level at 90% for most of the past three years, dropping it to 80% when the weather got really hot here in Houston. Last year I put air conditioning in the garage, so now it stays at 90% all the time. In three years I haven’t lost any battery capacity. 90% was 227 miles in May 2015 and it’s still 227 miles today.

 

[Arqui144]

So on 85kwh battery 90% is good? Also would anyone know how bad it is to charge to 100% if I will be driving wishing the next few hours?

 

[Veritas1980]

So on 85kwh battery 90% is good? Also would anyone know how bad it is to charge to 100% if I will be driving wishing the next few hours?

There is no data to suggest it is bad as long as you don't do it every day. Many people do this regularly without problems.
However, you may see better battery health over the total lifetime of the pack, how much I don't know.

Everything points to the 85 pack to be robust, so I wouldn't worry to much about it.

 

[Vern Padgett]

I have kept my charge level at 90% for most of the past three years, dropping it to 80% when the weather got really hot here in Houston. Last year I put air conditioning in the garage, so now it stays at 90% all the time. In three years I haven’t lost any battery capacity. 90% was 227 miles in May 2015 and it’s still 227 miles today.

That is fantastic Texas. All this obsessing about which level has been a waste of time is what it looks like! Keeping it between 20 and 80 I mean-- Maybe Tesla was right-- plug it in every night. Set it to 90% and don't worry.

 

[Fiver]

So on 85kwh battery 90% is good? Also would anyone know how bad it is to charge to 100% if I will be driving wishing the next few hours?

Charging to 100% is fine as long as you don't leave it at 100% for a long time. Usually charge to 100 right before starting a long drive, and overall the pack is fine. It's not necessary good for the pack, but overall filling it up, then driving somewhere isn't doing much harm.

Letting it sit at 100% all day or longer is a no no.

 

[brucet999]

So on 85kwh battery 90% is good? Also would anyone know how bad it is to charge to 100% if I will be driving wishing the next few hours?

Occasional 100% charge just before a trip does little damage, but rarely does it do any good. Only if there isn't a SC within reasonable range on your route, or if with the extra range you can save time by being able to bypass a SC, is it useful. Starting with a lower SOC gets you to your next SC with a lower SoC, thus speeding up the charge rate.

 

[TexasEV]

Occasional 100% charge just before a trip does little damage, but rarely does it do any good. Only if there isn't a SC within reasonable range on your route, or if with the extra range you can save time by being able to bypass a SC, is it useful. Starting with a lower SOC gets you to your next SC with a lower SoC, thus speeding up the charge rate.

Not this again! You can ALWAYS save time by starting your trip with 100% charge. When you get to the first supercharger, you have fewer miles to add to get to the target number of miles you want, when you start off with more miles. Arriving with a lower SOC may give you a higher initial charge rate, but the total charging time is greater if you’re needing to add more miles.

Example— which is a faster charge, arriving with 50 miles range and charging to 250 miles, or arriving with 100 miles range and charging to 250 miles?

 

[WattMobile]

Hi guys, I need some advice at how much I should have the cars SOC between. Today I charge everyday at work to 80% but I am thinking about lowering it to 70%. I drive under 60 miles one week and under 20 the next week (rotation). I still dont have a charger installed at my home but the weeks I drive around 60 miles I charge to 80% every day, and the week I drive under 20 miles I will charge it to 80% and let it stay in my garage which is in a cooled temperature. I would say around 62 Fahrenheit.

 

[Veritas1980]

Hi guys, I need some advice at how much I should have the cars SOC between. Today I charge everyday at work to 80% but I am thinking about lowering it to 70%. I drive under 60 miles one week and under 20 the next week (rotation). I still dont have a charger installed at my home but the weeks I drive around 60 miles I charge to 80% every day, and the week I drive under 20 miles I will charge it to 80% and let it stay in my garage which is in a cooled temperature. I would say around 62 Fahrenheit.

I would just keep it at 80% since you don't have charging at home, it's nice to have a little buffer for unexpected trips. I wouldn't think you would see any significant less battery degradation charging to 70 instead of 80%.

 

[ShockOnT]

Occasional 100% charge just before a trip does little damage, but rarely does it do any good. Only if there isn't a SC within reasonable range on your route, or if with the extra range you can save time by being able to bypass a SC, is it useful. Starting with a lower SOC gets you to your next SC with a lower SoC, thus speeding up the charge rate.

This feels right, but isn't.
Sure, getting to your next SC at 60% gets you faster charging than getting there at 70%, but only from 60 to 70%, which you wouldn't have had to bother with at all if you'd arrived at 70%.
Basically, it's always faster to leave with 100%.

 

[gavine]

This feels right, but isn't.
Sure, getting to your next SC at 60% gets you faster charging than getting there at 70%, but only from 60 to 70%, which you wouldn't have had to bother with at all if you'd arrived at 70%.
Basically, it's always faster to leave with 100%.

But when you start at a lower SOC and get that faster charge rate going, it gains momentum and blasts-through the taper

 

[lennyh]

This has likely been addressed previously, but I didn't see it. We are going way for three weeks without the Model S. Is it better to leave it on the charger or just let it sit in the garage without being plugged in. I generally charge to 70-75%.