Why is 80% charging recommended?

I just spent some time reading the (excellent) article here about Nissan leaf cars, battery degradation and other charging issues: http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss" onclick="window.open(this.href);return false;

It didn't help me understand the deal with the 80% charging recommendation. I thought based on the nissan website that the 80% charging limit was only for the 50a DC fast charging option which my car doesn't even have. I'm a bit dissapointed to hear that their official guidance is to charge the car to 80%, which cuts my effective range from 80mi to 65mi. That sucks, but i also don't want my battery to fail prematurely. (Even though Seattle is a great geography for Leaf batteries, I still want the car to perform great in 10+ years.)

Can someone on this forum provide a detailed breakdown of the reasoning for the 80% recommendations? Don't be shy, go into the engineering details if you like. I'm sure there are some real-world tests which have been performed in the field which informed this guidance.

Sincerely,
Tom (from Seattle!)

P.S. While I know there are some minor inaccuracies, I posted my initial experiences with the Leaf to my blog at http://tomalphin.com/2013/03/owning-an-electric-car-the-missing-manual.html Take a look, and post a comment if you like!

LiIon battery lifespan is improved if you cycle between the middle range of the battery (such as something like 25% - 75%). If you are always charging full to 100% and draining it to near 0%, battery capacity will suffer sooner than if you just use the middle range.


That's the same concept used in the Chevy Volt. They have a larger battery than what they make available to drivers, so they are just using the middle range of the battery pack for everyday driving...

You may want to do some reading on the Wiki:

http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss" onclick="window.open(this.href);return false;

Note that the graph above is for illustrative purposes only. It's from Stephen Moore's write-up on the iPhone, which you might find helpful as well. The values are not representative of what to expect with the Leaf, but hopefully the shape of the curve is. Perhaps it's worth noting that the iPhone uses a different lithium-ion chemistry, but the characteristics and behavior in terms of the charging protocol, and the desire to keep the battery away from SOC extremes should be comparable.

Another important point is that Nissan does not allow drivers to charge the battery to its (physical) maximum potential. Likewise, it's not possible to completely discharge it. There are reasonable safety margins built in, and it's virtually impossible to get it wrong. What we are discussing is relative improvement in battery longevity over months and years, and not something critically important for the daily operation of the vehicle.

Even if you charge the LEAF to full, as long as it gets driven daily, the battery won't spend much time at high voltage, and the difference when compared to someone charging to 80% will likely not be very significant. Yes, there might be bit of a difference after couple of years or so, and the delta will get larger over time, if the LEAF continues to be charged to 100%, but it won't be immediately noticeable.

That said, you might want to take care not to park the LEAF with a full charge for days, weeks and months, because that could lead to noticeably quicker capacity loss. Nissan requires an annual battery check to be done, and I believe that they call out number of things, such as prolonged storage at high state of charge. The annual battery report is an educational tool for drivers.

There are several posters on the forum, and I believe that Stoaty is one of them, who have seen much better battery performance than others in their locale. It's been attributed to gentle driving and defensive charging practices. Unfortunately, the data is somewhat anecdotal, and difficult to validate. It's likely too early to tell, since the oldest LEAF in the fleet is little over two years old. As you have noticed, we have already seen the effects of high ambient temperature, but thats' a separate topic.

Stoaty said:

You may want to do some reading on the Wiki:

http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss" onclick="window.open(this.href);return false;

Click to expand...

The wiki is incredibly helpful, and a great place to start. I believe Tom already did that

When the battery is at its highest voltage, the electrolyte in the cells breaks down faster. So yes, the battery lasts longer at 80% than at 100%. But relax, because it's also a time dependent thing. So charging to 100% and then driving the car doesn't leave it at that level very long. What you don't want to do is charge it up all the way and then leave it sit for a week. So, there is a difference, but it isn't huge. The second piece of good news is that you live in Seattle, and the biggest enemy to battery life is high temperatures, something you won't be seeing much of.

Still, it's unfortunate they're still selling the cars without informing the owners of things like this.

Yep, I completely agree with gbarry42. I'm down in Portland and just rolled over 40k miles and finally picked up a state-of-charge gauge (the WattsLeft that you can find under the CAN-bus sub-board here) and was very happy to read that when the car is completely charged to 100%, the state-of-charge gauge shows 98.5% SOC. Definitely within my expectations for two years of ownership under by belt!

^^^
How many gids? 276 or so?

henrysunset said:

I'm a bit disappointed to hear that their official guidance is to charge the car to 80%, which cuts my effective range from 80mi to 65mi.

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Actually, it's better than that and worse than that. I don't know what your 80mi is based on, but if it's a number you have read, your personal maximum mileage could be much higher or much lower depending on how or where you drive. Two other adjustments you will want to think about:

• Numbers like that are usually based on driving the car all the way down to empty, which is why I called it a maximum. You probably don't want to do that on a regular basis.
• This is a smaller point, but the distance from "80%" to "100%" isn't as much as you think, because the numbers are not comparable. 100% is the maximum the car will let you charge to, which is less than the total battery capacity. 80% is relative to the total capacity, so is really around 85% of the maximum you can use.

Here's a recent thread with a variety of viewpoints and thoughts on 80% vs. 100% charging: Any reason NOT to charge to 100% on a leased LEAF?

A search for "80%" will turn up many other threads, some of which may be of interest to you.

Ray

Thanks to everyone who has been providing detailed information on Leaf topics. Special thanks to the creators of the Wiki and those who contribute to it.

I found the referenced Wiki article on Battery Capacity Loss extremely helpful. I came out of it with one question. Suppose you have a trip scheduled that will use about 75% of the battery. Your options are to charge to 80% and then discharge down to 5% or charge to 100% and discharge down to 25%. For simplicity let's assume there is no option to recharge during this trip.

From what I read it seems that it is better to charge to 100% *if* you will be starting the trip soon after the charge completes. This is because (per my understanding of the article) that charging to 100% isn't bad if: a) the temperature is moderate and b) you don't leave the car at that SOC for very long. However, discharging down to 5% is a lot worse for battery life than discharging down to 25%.

Does this match the understanding of the experts on this forum? If so then I think we'll revise our practices to charge to 100% just before long drives. This has the added advantage of providing flexibility in the event of changes in plans.

For the record, our climate is probably somewhat colder on average than Toronto, using that chart there (we're at a significantly higher elevation than Denver). Temps top 90F only a few days per year and the cars are garaged at home.

cgaydos said:

From what I read it seems that it is better to charge to 100% *if* you will be starting the trip soon after the charge completes. This is because (per my understanding of the article) that charging to 100% isn't bad if: a) the temperature is moderate and b) you don't leave the car at that SOC for very long. However, discharging down to 5% is a lot worse for battery life than discharging down to 25%.

Does this match the understanding of the experts on this forum? If so then I think we'll revise our practices to charge to 100% just before long drives. This has the added advantage of providing flexibility in the event of changes in plans.

Click to expand...

Yes, this is what I do about once a week. I allow a couple of extra hours plugged in for battery balancing. There is no evidence that charging to 100% an hour or two before you leave for a long trip is harmful to the battery, especially if the temperature is not elevated. Remember that it is time and temperature at high state of charge that isn't good for the battery.

cwerdna said:

^^^
How many gids? 276 or so?

Click to expand...

I believe it was either 275 or 276.

henrysunset said:

I just spent some time reading the (excellent) article here about Nissan leaf cars, battery degradation and other charging issues: http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss" onclick="window.open(this.href);return false;

It didn't help me understand the deal with the 80% charging recommendation. I thought based on the nissan website that the 80% charging limit was only for the 50a DC fast charging option which my car doesn't even have. I'm a bit dissapointed to hear that their official guidance is to charge the car to 80%, which cuts my effective range from 80mi to 65mi. That sucks, but i also don't want my battery to fail prematurely. (Even though Seattle is a great geography for Leaf batteries, I still want the car to perform great in 10+ years.)

Can someone on this forum provide a detailed breakdown of the reasoning for the 80% recommendations? Don't be shy, go into the engineering details if you like. I'm sure there are some real-world tests which have been performed in the field which informed this guidance.

Sincerely,
Tom (from Seattle!)

P.S. While I know there are some minor inaccuracies, I posted my initial experiences with the Leaf to my blog at http://tomalphin.com/2013/03/owning-an-electric-car-the-missing-manual.html Take a look, and post a comment if you like!

Click to expand...

Lecture 1:
http://youtu.be/ZRVKXW3AqX0?t=1h18m14s" onclick="window.open(this.href);return false;

Lecture 2:
http://youtu.be/JgQc7KGJKdw?t=38m14s" onclick="window.open(this.href);return false;

cgaydos said:

Suppose you have a trip scheduled that will use about 75% of the battery. Your options are to charge to 80% and then discharge down to 5% or charge to 100% and discharge down to 25%. For simplicity let's assume there is no option to recharge during this trip.

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Well, as I said in my previous post, "80%" is really more like 85% of usable capacity, so your hypothetical 75% use would drop you to about 10%, not 5%. However, you never know exactly how much you are going to need. If, for example, the wind comes up, you are going to use more energy at the same speed. Or if you get a late start, you may feel the need to drive a bit faster. Traffic, temperature, and precipitation are among the other factors that can affect your range.

The plan I set for myself is not to drop below LBW, which is at about 17%. That leaves me a considerable margin for unexpected loss. 85% to 17% is 68% use. My rule of thumb is that if I expect to use more than 2/3 of the battery, then I charge to 100%.

Ray

DarkStar said:

I'm down in Portland and just rolled over 40k miles and [...] the state-of-charge gauge shows 98.5% SOC. Definitely within my expectations for two years of ownership under [my] belt!

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And, you've been babying that thing since you got it, right? :lol:

planet4ever said:

The plan I set for myself is not to drop below LBW, which is at about 17%. That leaves me a considerable margin for unexpected loss. 85% to 17% is 68% use. My rule of thumb is that if I expect to use more than 2/3 of the battery, then I charge to 100%.

Click to expand...

Ok, being a Leaf newbie (well, I've had one for almost 4 months, but I'm new to the forum) I first had to look up LBW. No, not "leg before wicket", but "low battery warning". Then I see LBW referenced in several tables and quotes near the bottom of the Wiki page.

Seriously? The main thing we have to do is avoid LBW? Gee, that's easy. We've been doing that all along. I guess we understood that even at 0 miles on the GOM that there was a decent reservoir remaining but never wanted to push that.

So, let my try to sum up the important things to do to maximize battery life - and any experts please correct and amend as needed:
1) Live in a moderate climate. Seriously, extreme heat seems to be the biggest factor. All those Leaf drivers in Norway know what they are doing. If your battery heat gauge shows 5 or fewer bars for all but a few days of the year at 6 you're in good shape. The table in the Wiki page regarding the difference in expected battery life between Dubai and Alaska - or even just between AZ and Quebec - is stunning.
2) Don't charge up to 100% unless the temp is moderate and you'll be starting on a longish trip shortly thereafter.
3) Don't let the battery get down to the low battery warning (LBW).

There are a number of other things you can do but those seem to be the main ones.

If that's right we're already set for (1) and (3), and except for a couple of snow days where we charged to 100% then didn't run the Leafs 'til the next day we're set on (2) - I can correct that moving forward.

cgaydos said:

3) Don't let the battery get down to the low battery warning (LBW).

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I would say that avoiding going below LBW is a reasonable thing to strive for, but the main thing after going fairly low on charge is to wait an hour for the pack to cool down, then charge up to the sweet spot (30-40% SOC). From LBW, an hour of L2 charging time will get you to around 35% Gids (which isn't the same as SOC, but close enough). That is a good state to leave the battery pack in when you aren't planning to drive anywhere for a while.

I agree that if the choice for a particular trip is to charge to 100% or go below LBW, I would opt for 100% charge (completed shortly before the trip begins).

cgaydos said:

planet4ever said:

The plan I set for myself is not to drop below LBW, which is at about 17%. That leaves me a considerable margin for unexpected loss. 85% to 17% is 68% use. My rule of thumb is that if I expect to use more than 2/3 of the battery, then I charge to 100%.

Click to expand...

The main thing we have to do is avoid LBW? Gee, that's easy. We've been doing that all along.

Click to expand...

No, you misunderstood me. I plan not to drop below LBW, while knowing that my plans are often not going to go perfectly. I have actually gone below LBW more than a hundred times, and below VLBW (three dashes on the GOM) more than a dozen times. That's why I said LBW leaves me a considerable margin. There is a knee in battery voltage at approximately VLBW, so I suspect that going below that point is rough on the battery, but I'll do it if I have to to make it home or to a charging station.

Ray

Stoaty said:

I would say that avoiding going below LBW is a reasonable thing to strive for, but the main thing after going fairly low on charge is to wait an hour for the pack to cool down, then charge up to the sweet spot (30-40% SOC).

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I'm not sure I agree with that (at least if you don't have to go anywhere). From what my research has shown, storage of lithium batteries at low SOC (even nearly completely empty - some Lithium chemistries can even be stored empty) is not detrimental, but discharge the pack at high rates when the SOC is low is harder on the pack.

To maximize life, try to avoid high power draw as the battery gets very low. But don't necessarily worry about charging soon unless you need to go off on another drive before your next scheduled charge, or perhaps if you did hit turtle and don't expect to be charging for at least a couple days.

cgaydos said:

Your options are to charge to 80% and then discharge down to 5% or charge to 100% and discharge down to 25%. For simplicity let's assume there is no option to recharge during this trip.

Click to expand...

My non-technical answer is, avoid the stress of having all those warnings going off when you are "trying to make it home". Unless you routinely drive the route (and are therefore familiar with the results) or have nerves of steel, it's just better to have a little reserve at your disposal. You have to consider your own well-being as well as the car's. Which is more important?

On the technical side, I would say that unless this is a routine trip, don't overthink it. Things you do infrequently just aren't going to add up to battery damage. And if it is a routine trip, start from 100% initially, and you'll learn what is really required and can back it off to 80% if it makes sense.

Thanks for the further clarifications, Stoaty, planet4ever, drees, and gbarry42.

I think I'll go with the consensus which is 100% charge shortly before starting on the trip. We have numerous round trips of 40-50 miles where we live, and sometimes need to detour for something on the way home.

And the advice for what to do when at LBW make sense - drive more moderately to reduce battery stress.

New question: is there any research on whether battery life is affected by using level 1 vs level 2 charging?