Better to use free charging to 100%?

[guythall]

When charging at home on my dime, i typically charge to 80%, unless i have special plans requiring more the next day. I know this should preserve battery life, but I'm clueless as to how much, and how to convert that to a financial cost.

Why is that important? My wife works at night at a business that allows her to charge our LEAF. So, she's been charging there to 100% using the "free" electricity. We've been presuming that the impact on battery life is very low, but honestly we have no idea.

I'm rashly assuming that cost to charge the last 20% of the battery charge is about:
= 20% * 24KWH / "efficiency factor" * $/KWH.
= 4.8KWH * $0.12 / KWH / "efficiency factor"
= $0.58 / "efficiency factor"
= $0.60 to $0.65

Compared to ??? How would you financially compare the extra 20% charge for free against battery wear?

Guy

 

[EdmondLeaf]

There is no real life data on 80 vs. 100% charge on battery degradation. Just charge, drive, and don't worry about it.

 

[mitch672]

I would also think, even if she charges to %100 at work, she is going to have to drive the car home, when you get it home, it's not going to have that %100 charge left, so probably not worth worrying about at all.

 

[thankyouOB]

I have the same decision to make because of trickle charging avail at work and I have decided to pick the percent of charge without regard for whether I am doing it free at work.

The savings is pretty tiny, and do recall that it is already a huge savings off of the cost of gasoline to commute.
I just dont see the gain in getting two more bars free (prolly 12-14 miles or about 25 cents worth) even five days a week ($50-60 a year) at any risk to battery life.
I do charge to 100% when I need the range, especially if I am taking a trip around before going home after work.

 

[ebill3]

There is no real life data on 80 vs. 100% charge on battery degradation.

Are you quite sure that is a correct statement?

Presumably, Nissan engineers know quite a bit more about the care and feeding of Li-Ion batteries than you or me, and they strongly recommend 80%.

Bill

 

[baronvonshush]

I would just look at how much charge/range you'll need before the next time you charge at the free station. If you'll use less than 80% before the next time you get a free charge, no need to get that extra 20% now, right? Basically the same strategy you already have for home charging.

I also charge for free at work, and most days I charge to 80% because that's way more than enough to cover the 40-mile roundtrip commute. Even on days when I have an extra 30 miles of driving after work, I've found that 80% leaves me enough range to spare. About the only time I charge to 100% is on the last day of the week, maximizing free electrons for the weekend.

 

[davewill]

My feeling is if work is nice enough to offer free EV charging, we should treat it as if we WERE paying for it. To me, it's much the same as filching office supplies, hogging all the donuts or filling my thermos up with office coffee just because I can. For the EV, that means not changing from 80% to 100%, or skipping charging at home just to take advantage of free juice.

Besides, like the coffee, the savings to an individual is pretty small, but cost to the company if lots of employees (looking a little forward I admit) did it is large.

 

[DaveEV]

There is no real life data on 80 vs. 100% charge on battery degradation.

Are you quite sure that is a correct statement?
Presumably, Nissan engineers know quite a bit more about the care and feeding of Li-Ion batteries than you or me, and they strongly recommend 80%.

EdmondLeaf should have clarified his statement saying that there is no public data. Nissan for sure has the data.

IMO - unless you need the range - charge to 80%, free or not. Better to be conservative than to risk accelerated capacity loss!

Not to mention the other benefits:

* Charging to 80% is more efficient - charging efficiency drops in the last 30 minutes when charging to 100%
* Driving at 80% is more efficient - you get no to very little regen the first 10 miles or so after a 100% charge.
* Charging at home during off-peak hours (midnight-6am) is more efficient - the grid is under utilized at that time - charging at that time increases grid efficiency by reducing the amount of ramping power plants have to do.
* Those "free" electrons are not really free. Someone is paying for them and likely paying more for them than you do charging at home.

FWIW - the extra energy that goes into a 100% vs 80% charge is about 4.5-5 kWh. Or about $0.50-$1 worth of electricity depending on rates. Never mind that unless you have a long commute, most could probably do the entire trip on an 80% charge if you're that cheap!

 

[EdmondLeaf]

There is no real life data on 80 vs. 100% charge on battery degradation.

Are you quite sure that is a correct statement?

Presumably, Nissan engineers know quite a bit more about the care and feeding of Li-Ion batteries than you or me, and they strongly recommend 80%.

Bill

IMO if benefit of 80% is well known (to Nissan engineers), therefore we will have that number in manual. If in your opinion there is only one factor that affect degradation of the battery, I would like to know. Nissan give us general guidelines how to reduce degradation, but calculation exact number IMO is impossible. I very much would like to know what will be battery capacity after limited battery warranty expire, I only charge to 80%?
After all OP want to know what is the cost benefit, so number is needed. Next thing we do not know, how much replacement battery will cost, so such calculation is impossible at present time.

 

[thankyouOB]

My feeling is if work is nice enough to offer free EV charging, we should treat it as if we WERE paying for it. To me, it's much the same as filching office supplies, hogging all the donuts or filling my thermos up with office coffee just because I can. For the EV, that means not changing from 80% to 100%, or skipping charging at home just to take advantage of free juice.

Besides, like the coffee, the savings to an individual is pretty small, but cost to the company if lots of employees (looking a little forward I admit) did it is large.

nicely put.
dont bite the hand that feeds you.
greedy pigs get slaughtered.

 

[coqui]

Office supplies vs coffee vs charging is not the same thing.
Taking office supplies home is stealing. Not gonna do that.
Coffee is a benefit, supplied by the employer, and made clear at the time of employment that it is free to employees and business guests.
Charging (if we had it here) would also be a benefit. At $0.65 a day I daresay it may even be cheaper than that coffee!
Some employers in downtown areas provide parking free. Its a benefit. In New Orleans (and I'm sure elsewhere too) that can amount to several hundred $ a month.

 

[Volusiano]

I would just look at how much charge/range you'll need before the next time you charge at the free station. If you'll use less than 80% before the next time you get a free charge, no need to get that extra 20% now, right? Basically the same strategy you already have for home charging.

I also charge for free at work, and most days I charge to 80% because that's way more than enough to cover the 40-mile roundtrip commute. Even on days when I have an extra 30 miles of driving after work, I've found that 80% leaves me enough range to spare. About the only time I charge to 100% is on the last day of the week, maximizing free electrons for the weekend.

I'm with this school of thought. Why charge the extra 20% unless you need it during that 24 hour period?

For example, if you charge to 100% and the next day you come back at 40%. It'd be the same as charging to 80% and the next day you come back at 20%. Each day, you only use 60% regardless.

If each day you use 80% or more, then I can see the need to charge to 100%.

If you use between 60%-80% usage each day, then you'll have to decide how much margin you'd like to have left over for unplanned side trips.

 

[davewill]

Office supplies vs coffee vs charging is not the same thing. ...

Perhaps not, but abusing the privilege still seems like a bad idea to me.

 

[lpickup]

Why charge the extra 20% unless you need it during that 24 hour period?

Thank you for saying this! I was thinking the same thing but couldn't find a way to put it into words. You did so perfectly!

 

[ebill3]

There is no real life data on 80 vs. 100% charge on battery degradation.

Are you quite sure that is a correct statement?

Presumably, Nissan engineers know quite a bit more about the care and feeding of Li-Ion batteries than you or me, and they strongly recommend 80%.

Bill

IMO if benefit of 80% is well known (to Nissan engineers), therefore we will have that number in manual. If in your opinion there is only one factor that affect degradation of the battery, I would like to know. Nissan give us general guidelines how to reduce degradation, but calculation exact number IMO is impossible. I very much would like to know what will be battery capacity after limited battery warranty expire, I only charge to 80%?
After all OP want to know what is the cost benefit, so number is needed. Next thing we do not know, how much replacement battery will cost, so such calculation is impossible at present time.

Well, of course, the 80% is in the manual. And, I certainly am not suggesting that there is only one factor that affects battery life. High temperature, deep discharge, and heavy current drain are a few more.

It is not just Nissan engineers that are aware of the benefits of reduced SOC. Li-Ion cells have been around for a long time - well before the LEAF hit the test track. Plenty of time to amass real world longevity data. But, apparently Nissan is so convinced that reduced SOC is beneficial, that the BMS only allows cells to be charged to 4.1 volts, while 4.2 volts is usually accepted as maximum charge for a Li-Ion.

As to the OP's quandary, I think the saving of a few cents now is penny wise and pound foolish.

Bill

 

[TEG]

For what it is worth, Tesla also recommends not "fully" charging their vehicle's packs unless you really need the full range.

 

[Cheezmo]

I slightly different angle from an evGo subscription customer. Since I'm paying monthly for unlimited use of their chargers, I kind of feel obligated to top off (at least to where it slows down substantially) every time I drive by their DC fast charge stations to get the most kWh for the money I'm paying.

Are all those "partial fast charges" going to be bad for my battery? I'm on a 3 year lease, should I even care?

 

[smkettner]

If you are going to occupy the space you may as well go 100%.
If there is an abundance of EVs waiting to charge then by all means grab only what you need.

 

[DaveinOlyWA]

charging to 100% is really only detrimental if you plan to leave it 100% for extended periods of time. i went from charging to 100% 1-2 times a week to charging to 100% nearly every day due to changes in my commute so the long term effects remain to be seen but what about our 36,000 mile man?? who has charged to 100% TWICE A DAY 5 days a week for a week short of a year with no apparent (has no meter) degradation of range?

only verifiable Leaf with permanent degradation of range was one that was purchased as a demo. guessing the demo was charged to 100% and sat there for maybe a day or two before someone thought to drive it is the main reason the degradation has happened.

as for me? take advantage of the freebies your employer provides while its available. charging to 100% then driving home means a very short time at 100%. just dont charge when you get home if you dont have a lot of driving to do

 

[surfingslovak]

We had this discussion many times before, and I'm firmly in the "charge to 100% if you need it or want it" camp now. Sure, the battery will see less pronounced gradual degradation if it's charged to a lower potential. This might be particularly worthwhile when the car is sitting all day in a hot parking lot, or for storage. For the daily commute, I would just charge any way I want, and be happy. If you would prefer to charge to 80%, that's OK too.

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