Is it better for my car to spend more time at 50% or have shallower discharge cycles but spend more time at a higher state of charge.

[J-a-x]

I work from home and usually do one large drive each weekend. I live in a condo with a shared charger so its inconvenient to charge after every drive because I have to move my car once the charge is complete, therefore I have not been charging every day like Tesla recommends.

My current charging strategy is to charge up before each long trip (leaving home tat 90 or 100%) and then supercharge on the way home such that I get home with around 50% charge. This way my car sits in the garage during the week close to 50% with a few small city trips and errands running it down to about 40% before I charge back up to either 90% or 100% before another long trip and repeat. Whenever I do the charge up to 90 or 100 I drive immediately so it’s not spending much time over 50%.

My thought is that if I keep the car between 40-50% when its (mostly) sitting at home during the week, and only charge it up immediately before my trip (lets say 40% to 90%) it maximizes the time my car spends around 50% (give or take) and minimizes the time it sits at higher levels of charge.

I was wondering today whether this strategy is ideal Maybe what I should do is charge immediately after returning home to 75% and keep charging back to 75% after each small trip. In this scenario I would limit the depth of any one charge cycle, but this would also mean spending more time >50%.

So I’m just curious if it’s better for the car to have smaller discharge cycles, or is it better for the battery to spend most of its time around 50%. I know that both deep cycles and time spent at higher states of charge can cause degradation but I’m curious which scenario is the best for long term battery health.

 

[LoudMusic]

Smaller discharge/charge sessions are apparently less harmful to the battery. Keeping the battery between 20 and 80 percent seems to be the popular recommendation these days.

If you like exceedingly nerdy videos, check this one out.

My personal concern with storing the vehicle with too low of charge is that in my particular scenario I don't have many options for quickly getting the state of charge up to a high value. My daily usage is typically 25 to 30 %, but occasionally I have impromptu days of 50% or more. If I start the day at 50% and burn 15% commuting or running errands, I wouldn't even have enough to get to the nearest Supercharger. I'd be stuck at an L2 charger for an hour+ just to make the trip to the Supercharger, which may not even be in the direction of my actual destination. So I plug in when I get home and have the car set to 80%.

It appears you're in Boston and there are many more fast charging options for you there. 50% might be fine, and seems to be enough to cover your trips.

 

[J-a-x]

Yeah I feel like i dont get range anxiety at 50% since can charge at a whim in my garage’s shared charger (albeit slowly at 6 kw) if I have something coming up. There are superchargers on the major highways heading out of town but frankly I’m surprised how rare DC fast charging is around here. 6 kWh are everywhere though. I think that will change in the next couple years, I see 50 kW DC replacing some of the ubiquitous 6 kW chargers eventually.

You say lots of small chargers is bad? I always heard that was preferable to less but deeper charges! I guess my “middle ground” approach is probably ideal because it combines a medium discharge cycle with most hours spend around 50…

 

[E90alex]

I believe storage SoC has a bigger effect on degradation than DoD. So in other words stick with what you’re doing with 50% mode of the week.

 

[J-a-x]

I believe storage SoC has a bigger effect on degradation than DoD. So in other words stick with what you’re doing with 50% mode of the week.

Thank you!

 

[LoudMusic]

Yeah I feel like i dont get range anxiety at 50% since can charge at a whim in my garage’s shared charger (albeit slowly at 6 kw) if I have something coming up. There are superchargers on the major highways heading out of town but frankly I’m surprised how rare DC fast charging is around here. 6 kWh are everywhere though. I think that will change in the next couple years, I see 50 kW DC replacing some of the ubiquitous 6 kW chargers eventually.

You say lots of small chargers is bad? I always heard that was preferable to less but deeper charges! I guess my “middle ground” approach is probably ideal because it combines a medium discharge cycle with most hours spend around 50…

No no, small charging is good! Plug in whenever you can and put back whatever little bit you used.

 

[KenBlub]

For the first 6-7 years a lower SOC produces way less battery degradation than charging cycles. If you can’t easily charge at home, what you are doing is best.

 

[tgrobbo]

For LFP I’m pretty sure Tesla recommend 50% SOC for long term storage somewhere deep in some service manual. Not sure if it’s the same for other chemistries. You are lucky to be able to keep it around 50% most of the time, as many just can’t practically do that with their cars. I have to leave mine sitting at 100% overnight quite a bit - which always bothers me a little!

 

[J-a-x]

For LFP I’m pretty sure Tesla recommend 50% SOC for long term storage somewhere deep in some service manual. Not sure if it’s the same for other chemistries. You are lucky to be able to keep it around 50% most of the time, as many just can’t practically do that with their cars. I have to leave mine sitting at 100% overnight quite a bit - which always bothers me a little!

What I gain by leaving my car at 100% I lose by having a bit more depth of charge I guess. Not sure who comes out ahead...

I rarely do 100% overnight but always wondered if that was a bed idea. I usually sacrifice a bit of range by usually starting trips at 90% for that reason (I'm less worried about 90% overnight).

I usually do 100% at some point on a road trip if I'm at a charger and want to have a longer stop for a meal, but then leave immediately after.

No no, small charging is good! Plug in whenever you can and put back whatever little bit you used.

sorry I think I read your original post wrong. Yeah we're on the same page, lots of little charges is good, except I can't do that due to my annoying HOA.

 

[KenBlub]

I recommend you search for @AAKEE and his many discussions on these issues. You won’t find anyone, anywhere more knowledgeable

 

[AAKEE]

For LFP I’m pretty sure Tesla recommend 50% SOC for long term storage somewhere

15-50% on all Tesla batteries according to Teslas own statement in the EPA test protocols.

The lower the SOC, the lower the calendar aging.

 

[AAKEE]

No no, small charging is good! Plug in whenever you can and put back whatever little bit you used.

Keeping the calendar aging low beats cyclic aging anyway, as cyclic aging is the much smaller part of the degradation for the first 5-8 years.

The good thing is that there is no opposite relationship between cyclic aging and calendar aging.

This is how to think:
-Do not charge more than you need until the next charge.
-Charge often, lowers the need per above and gives small cycles.
-Charge late, reduces calendar aging.

Myths usually fool people to use wrong tactics, when trying to reduce degradation, here is the real fact:
- Below 20% is not bad for the battery.
- 100% is not dangerous for the battery.

 

[LostVector]

I work from home and usually do one large drive each weekend. I live in a condo with a shared charger so its inconvenient to charge after every drive because I have to move my car once the charge is complete, therefore I have not been charging every day like Tesla recommends.

My current charging strategy is to charge up before each long trip (leaving home tat 90 or 100%) and then supercharge on the way home such that I get home with around 50% charge. This way my car sits in the garage during the week close to 50% with a few small city trips and errands running it down to about 40% before I charge back up to either 90% or 100% before another long trip and repeat. Whenever I do the charge up to 90 or 100 I drive immediately so it’s not spending much time over 50%.

My thought is that if I keep the car between 40-50% when its (mostly) sitting at home during the week, and only charge it up immediately before my trip (lets say 40% to 90%) it maximizes the time my car spends around 50% (give or take) and minimizes the time it sits at higher levels of charge.

I was wondering today whether this strategy is ideal Maybe what I should do is charge immediately after returning home to 75% and keep charging back to 75% after each small trip. In this scenario I would limit the depth of any one charge cycle, but this would also mean spending more time >50%.

So I’m just curious if it’s better for the car to have smaller discharge cycles, or is it better for the battery to spend most of its time around 50%. I know that both deep cycles and time spent at higher states of charge can cause degradation but I’m curious which scenario is the best for long term battery health.

Because you aren't cycling the battery daily, leaving the battery at a lower state of charge during the week is probably the dominant factor in battery aging. But also, charging to 100% to arrive home with 50% is definitely going to wear your battery more quickly.

Parts of the battery literally expand ... and they expand the most when you go to 100%. It doesn't sound like you actually need to go to 100%, so I would recommend not doing it. It will definitely be easier on the battery.

Why not do 75 to 25? In general, cycling around 50% is a pretty good strategy.

 

[LikesToys]

The sweat spot for an NCA battery is 57%. If you are not using the car you should leave it close to that. If you plan a long trip and need the power charge it to your needs and drive off as soon as possible. Ideally you would not charge beyond 90% unless you require it. If possible don’t discharge the battery lower than 30%. I believe your current strategy is correct but as some have pointed out a 90-40% may be better than 100-50. Some of the other comments seem related to LPF batteries which I don’t think you have. I got my info from Dalhousie - several good YT videos:

. They are under contract to Tesla and did the basic science for their batteries.

 

[AAKEE]

The sweat spot for an NCA battery is 57%. If you are not using the car you should leave it close to that.

That is not correct.

Calendar aging for NCA is reduced quite much at or below 57-58%, but still lower SOC is better.
(Teslas buffer makes 57% real SOC to be 55% displayed so we should use 55% as the reference for upper limit if we like to reduce the degradation).

This has been tested many times in research. In general calendar aging vs SOC look like this: (Panasonic NCR18650 in this test). This picture is a specific test, but very good to use as a common way to look at calendar aging.

Here is cells taken from a Tesla model 3 cells (Panasonic 2170, NCA-cells):

This is actual model S cells, taken from a almost new ’16-17 S:

We can see that low SOC is very good to reduce calendar aging.
We also can se that 100% SOC is not at all as bad as the common myth.

If you plan a long trip and need the power charge it to your needs and drive off as soon as possible.

As you could see above, the above 80 or 90% being very bad is not true.

High SOC is worse at high temperature.

If possible don’t discharge the battery lower than 30%.

That is not correct. The batteries does get hur from low SOC.

If looking at small cycles, the lowest degradation from cycles happens around 35-55% SOC for actual Tesla model 3 cells.

This picture is from cycling Tesla model 3 cells in different SOC ranges.
It might look like the lower SOCs are very bad but, if we look at 5-15%, and 1000 FCE cycles (which in this case is 10.000 charges/discharges) we loose about 15%.
1000 FCE is about 400K km or 250K miles.
This means that driving the normal average 20K km or 15K mi we loose about 20/400x 15 = 0.75% per year in cyclic aging.

At the same time we loose about 5 % from calendar aging during the first year and about 10% in total after 4 years if mostly using SOC above 55% displayed.
Using 55% displayed mostly or at least having the car at or below 55% will cost about 2.5-3% the first year and 5-6% in total after four years.

So we can look at the uppermost picture above and see that as we reduce calendar aging at very low SOC, the slightly increased cyclic aging is more or less compensated by the lower calendar aging.

 

[LikesToys]

That is not correct.

Calendar aging for NCA is reduced quite much at or below 57-58%, but still lower SOC is better.
(Teslas buffer makes 57% real SOC to be 55% displayed so we should use 55% as the reference for upper limit if we like to reduce the degradation).

This has been tested many times in research. In general calendar aging vs SOC look like this: (Panasonic NCR18650 in this test). This picture is a specific test, but very good to use as a common way to look at calendar aging.
View attachment 1018271

Here is cells taken from a Tesla model 3 cells (Panasonic 2170, NCA-cells):
View attachment 1018272

This is actual model S cells, taken from a almost new ’16-17 S:
View attachment 1018274

We can see that low SOC is very good to reduce calendar aging.
We also can se that 100% SOC is not at all as bad as the common myth.



As you could see above, the above 80 or 90% being very bad is not true.

High SOC is worse at high temperature.




That is not correct. The batteries does get hur from low SOC.

If looking at small cycles, the lowest degradation from cycles happens around 35-55% SOC for actual Tesla model 3 cells.

This picture is from cycling Tesla model 3 cells in different SOC ranges.
It might look like the lower SOCs are very bad but, if we look at 5-15%, and 1000 FCE cycles (which in this case is 10.000 charges/discharges) we loose about 15%.
1000 FCE is about 400K km or 250K miles.
This means that driving the normal average 20K km or 15K mi we loose about 20/400x 15 = 0.75% per year in cyclic aging.

At the same time we loose about 5 % from calendar aging during the first year and about 10% in total after 4 years if mostly using SOC above 55% displayed.
Using 55% displayed mostly or at least having the car at or below 55% will cost about 2.5-3% the first year and 5-6% in total after four years.

View attachment 1018276

So we can look at the uppermost picture above and see that as we reduce calendar aging at very low SOC, the slightly increased cyclic aging is more or less compensated by the lower calendar aging.

Could you please state what to do, rather than stating what not to do. Thanks

 

[AAKEE]

Could you please state what to do, rather than stating what not to do. Thanks

- Do not charge more than you need* until the next charge. (Reduces the average state of charge)
- Charge often. (Reduces the needed level per above, and the cycle size).
- Charge late, so the car is ready shortly before the drive. In many cases, ready in the morning instead of starting the charge at arrival at home before dinner.
This reduces the average SOC and by that the calendar aging.

For cars with NCA chemistry, 55% displayed SOC or below is good.
For NMC, 60% or below.
For LFP, 70% or below.
(Could be slight differences within the same chemistry, but as a good base these will work).

*)The lithium batteries are not hurt by low SOC. Thats a myth. So, the lower limit should be your own reference for not getting range anxiety, and maybe safety precautions if very cold in the winter.
The battery is happy down to 0%, if you are.

( I do actually not think I wrote what not to do. I think I wrote what parts was not correct, with corrections and also examples from research)

 

[zoomer0056]

I was wondering today whether this strategy is ideal

I think what you're doing is the best way.

 

[J-a-x]

The sweat spot for an NCA battery is 57%. If you are not using the car you should leave it close to that. If you plan a long trip and need the power charge it to your needs and drive off as soon as possible. Ideally you would not charge beyond 90% unless you require it. If possible don’t discharge the battery lower than 30%. I believe your current strategy is correct but as some have pointed out a 90-40% may be better than 100-50. Some of the other comments seem related to LPF batteries which I don’t think you have. I got my info from Dalhousie - several good YT videos:

. They are under contract to Tesla and did the basic science for their batteries.

Thanks that was enlightening, and I love that it's Canadian !

 

[KenBlub]

Except that isn’t correct. Did you not read posts 15 and 17. To be precise, if you have a NCA battery, it’s best to be below 55% SOC as long as possible. Please look at the charts in post 15 and note the plateau at 55%.