The 30-60 rule

[shahryaran]

I'm writing this to help EV owners (specially new owners) to maintain the best balance between battery health and practicality.

Charging from 30% to 60% (level 1,2 or 3) is the best way to keep your battery healthy while practical in real life. A general rule is that only charge to the point that you need for that drive and 30-60 rule is the perfect spot.

These are the reasons why:
Shallow depth of charge.
Full functionality at lowest (30%) sentry mode, etc.
Enough charge at lowest for emergency drive.
Good rule for all weather.
Enough charge for a long drive at highest


And these are the sources if you are interested why:

https://www.researchgate.net/profile/Harry-Hoster/publication/349746567_High-energy_NCA_cells_on_idle_anode_versus_cathode_driven_side_reactions/links/603fdf2ba6fdcc9c780f62e6/High-energy-NCA-cells-on-idle-anode-versus-cathode-driven-side-reactions.pdf?origin=publication_detail

http://kth.diva-portal.org/smash/get/diva2:1755178/FULLTEXT01.pdf

https://mediatum.ub.tum.de/doc/1355829/file.pdf

Is battery calibration pointless?!

Let's say your car has some amount of battery degradation and you can't get the range you want. You were told to calibrate battery and you may get some range back. Here is the thing... It doesn't matter and don't worry about it. The fact is that the actual amount of battery capacity is there...

teslamotorsclub.com

 

[Sorny]

Yeah, no.

I use >30% one way to work in the winter. Sometimes, it's ~40-45% one way when it's cold and windy. I was charging to 100% and arriving home at 5-8% for a week straight so far this winter when it was both cold and windy.

Even in the summer, charging to 60% would have me in single digits on return home.

Maybe, just maybe, your general "rules" are too general to be of specific use to anyone that actually has to drive, or lives where there are 4 actual seasons.

 

[shahryaran]

Yeah, no.

I use >30% one way to work in the winter. Sometimes, it's ~40-45% one way when it's cold and windy. I was charging to 100% and arriving home at 5-8% for a week straight so far this winter when it was both cold and windy.

Even in the summer, charging to 60% would have me in single digits on return home.

Maybe, just maybe, your general "rules" are too general to be of specific use to anyone that actually has to drive, or lives where there are 4 actual seasons.

Obviously you should charge as much as you need.

 

[AAKEE]

If you do not need sentry or any of the things that disables at 20%, you can go lover in SOC without any issues.

Remember that cyclic aging is very low anyway (and even it if differs, the difference is lower than the calendar aging).

For NCA it will be good to stay at 55% and below. The time spent at 60% will cause much higher degradation than 55% so if you need 30% between two charging sessions, 55-25% is better than 60-30%.

Lowest degradation will come from reducing time above 55% displayed SOC ( = 57% true SOC).

So this is the mantra to remember:
1) Do not charge more than you need.
2) Charge often (reduces the need in the first rule)
3) Charge late. Reduces the degradation from time, and specially if going above 55%.

Add-on to these rules:
-The battery is as fine at 100% as at 80%, for example overnight etc, but when needing > 55% charge as late as possible.
Charging to 100% and driving asap gives very low degradation so we can do 100% any time we need.
-The battery is fine at 0%, and there is not increased degradation below 20% as the myth says. The lower end of SOC for daily or trip is the range anxiety limit, which is a personal limit rather than the battery.

 

[LarryClay]

Near 0% SOC and very cold weather do not mix gracefully.

Proposed rules work fine in hot climates, where also calendar aging is high. But may break apart in cold weather where calendar aging is already low.

When temperatures drop below freezing point, effective capacity of LiXXX batteries can drop even 40% compared to hot weather. At the same time energy consuption doubles. So your capacity factor gets: 0,6 * 0,5 = 0,3.

You left your car with 20% SOC remaining during cold winter?
When battery cells cool down you get 20 * 0,3 = 6% of effective full range. And then you have a Chicago Tesla Winter Syndrome. Not fine at all.
Common sense should be excercised during winter/cold weather.

In freezing cold winters I would keep bottom 20% SOC as minimal buffer.

 

[AAKEE]

Near 0% SOC and very cold weather do not mix gracefully.

We need to be clear with what aspect we use. Range or battery life.

If we have too low SOC when we are about to drive away of course the range can be insufficient.
Teslas 20F test shows that for a full pack we loose about ~ 7% energy output compared to the normal warm test.

Tesla deliberately show a lower SOC on the car when the battery is cold to compensate for the lower energy output.

But for the sale of the battery there is no danger to drive it well below the usual 20% forum myth limit.

I live at the artic circle with extreme cold during the winter. So far coldest -41C (about -40F as well) where I had my car parked outside with ~ 11% at work

Last week we had -30C and the car was parked with low SOC at work.

A scheduled departure or just starting the cabin heat will warm the battery above the freezing level so it will accept regen.
This might cost some energy depending om how cold and how long the car was parked.