Ways to preserve battery capacity (besides charging to 80%)?

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jason98

Well-known member
Joined
May 24, 2010
Messages
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I believe, battery degradation is one of the primary concerns for me as an electrical car owner.

-Are there any official/non-official tips, driving habits? Any reference documentation from Nissan?
-What is the optimal top charge? (80% or maybe lower?)
-What is the optimal discharge level? (Is it better to fully discharge the battery before charging again? Or is it better to recharge it as soon as you reach a charger?)
-Preferred charging: L1, L2, or L3? (Is the quick charge bad for the battery?)
-To ECO or not to ECO? (ECO mode seems to use regenerative braking a lot. Is it bad for the battery?)
-Optimal speed? (Again optimal not for efficiency but for capacity preservation)
 
Jason,
Here are my comments regarding your question, based on my research on Li-ion batteries.


-Are there any official/non-official tips, driving habits? Any reference documentation from Nissan?
Don't know

-What is the optimal top charge? (80% or maybe lower?)
Probably a good upper SOC. My 2002 Prius battery (not Li-ion but NiMH) does not charge above about 80% to preserve life.

-What is the optimal discharge level? (Is it better to fully discharge the battery before charging again? Or is it better to recharge it as soon as you reach a charger?)
Probably 40% SOC is good lower level to preserve life. Certainly lots of full discharge cycles is not good for battery life. The time between discharge and recharge may not be too important if the temperature is not high. If the battery temperature is high, it would be better for the battery to cool down prior to recharge.

-Preferred charging: L1, L2, or L3? (Is the quick charge bad for the battery?)
L1 is the best for battery life. The lower the charge rate, the closer to reversible capacity that will be obtained, and the less stress the battery will experience.

-To ECO or not to ECO? (ECO mode seems to use regenerative braking a lot. Is it bad for the battery?)
Not sure if regen is bad for the battery if the charge rate is not too high and the battery temp. is not too high. Also depends on what you mean by bad. Most batteries used in a SOC range that is not too high or too low yield maximize battery life. So if regen occurs at SOC in the range of 40-80%, then this should not be bad for the battery.

-Optimal speed? (Again optimal not for efficiency but for capacity preservation)
Lower discharge rate of the battery is better, so lower speed should be better for capacity preservation.

Still waiting for my LEAF so I have no first-hand-experience with an EV powered by Li-ion batteries.
 
linkim said:
-Preferred charging: L1, L2, or L3? (Is the quick charge bad for the battery?)
L1 is the best for battery life. The lower the charge rate, the closer to reversible capacity that will be obtained, and the less stress the battery will experience.
Click to expand...
From what I've read here and elsewhere I would disagree with this. My understanding that the 240V/L2 charging is still very slow/low from a battery standpoint. I get the impression that the only one that is "bad" for the battery is the DC quick charge. I would imagine even when the Leaf goes to the 6.6kW AC charge, it still won't be a problem with the battery when it comes to lifespan.
 
Jason,
Please note my comment "The lower the charge rate, the closer to reversible capacity that will be obtained, and the less stress the battery will experience."

I did not respond directly to your question. There is some data which I will dig up and sent to you PM regarding the effect of charge rate.

Certainly the QC option is not good. What the adverse effect of L2 on battery life will be, that will become available with more data from the LEAF.
 
linkim said:
Jason,
Here are my comments regarding your question, based on my research on Li-ion batteries.

-What is the optimal top charge? (80% or maybe lower?)
Probably a good upper SOC. My 2002 Prius battery (not Li-ion but NiMH) does not charge above about 80% to preserve life.

-What is the optimal discharge level? (Is it better to fully discharge the battery before charging again? Or is it better to recharge it as soon as you reach a charger?)
Probably 40% SOC is good lower level to preserve life. Certainly lots of full discharge cycles is not good for battery life. The time between discharge and recharge may not be too important if the temperature is not high. If the battery temperature is high, it would be better for the battery to cool down prior to recharge.
Click to expand...

If we compare to Prius, let's not forget that what's good for NiMH could be bad for Li-ion and vice-versa.
 
I agree there are differences between the Li-ion (nonaqueous electrolyte) and NiMH (aqueous electrolyte) batteries, but I think the general principle regarding the "sweet spot" for SOC range to extend battery life is still applicable. Charge-discharge of a battery between 0% and 100% is an extreme, and this range is often used as one metric for cycle life. Cycling to a smaller SOC range is typical, and leads to improved cycle life.
 
Charging the battery to 80% at a slow rate, in cool temperatures, has the best chance of prolonging its life. Since Nissan never allows the battery to be charged up to 100% (the real capacity is more than 24kwh), charging up to 80% is actually a lower SOC, perhaps as low as 65%.. and this is a very gentle treatment of the battery. Discharging the battery down to zero also decreases its life, it heats up.. so only charge it to 80% and recharge it when it gets down to 30 miles remaining (guess), at night when its cool then that is your best hope. Recharge your battery every night, its not good for it to be below 50%.

Fast charging in itself does not hurt the battery, the excess heat does. There are two kinds of L3 charging, the one you start when the battery is low and brings it up to 80% in 30 minutes, the second one the battery is at 50% (I think) and the L3 charge brings it up to 100%.. the 100% will create a lot more damage than the first one. But dont be paranoid about the occasional L3 charge.. the battery will still last 8-10 years.

It is possible that some people in cooler climates (Seattle?) will have longer lives than this, perhaps into the 200-300k mile range.

If you do everything right you will be still driving your original Leaf battery when everyone else is driving the 1000kwh lithium metal packs powered hovercrafts, you will be as obsolete as driving a Model T on the hwy :)
 
Herm said:
But dont be paranoid about the occasional L3 charge.. the battery will still last 8-10 years.
Click to expand...

That's promising. Wonder why computer/consumer electronics batteries are so bad. My Dell laptop's last only one year on average.
 
jason98 said:
Herm said:
But dont be paranoid about the occasional L3 charge.. the battery will still last 8-10 years.
Click to expand...

That's promising. Wonder why computer/consumer electronics batteries are so bad. My Dell laptop's last only one year on average.
Click to expand...

Those cells are treated very cruelly so that the manufacturer can claim a high run-time, and enjoy a minimal build cost. A year later they have your money and you accept replacement as a fact of life.

The Apple notebooks claim a 5-year battery lifespan. Not because they have some alien chemistry, but because they are very careful with the charging/discharging protocol on a per-cell basis and treat the cells well.
 
I import lithium, build management systems and small packs, and my daily driver is a lithium-filled motorcycle. Based on both study and real world experience on the bench and on the street, I'll start by saying to completely ignore anything about the Prius or any other hybrid car.
- they don't use lithium (yet!)
- their cells are tailored for intermittent bursts of power rather than lifespan
- they're severely over-managed because the hybrid battery is part of the emissions control system in the car (and the nature of the power cell VS. energy cell)

Nissan only allows us to use 80-84% of total capacity. LiMn, like LiCo/LiPo, carries it's energy higher in the charge/discharge curve, so the ~80% we can use is slightly higher than middle (likely 95% to 15% rather than 20-80%). This range is already selected to give a long battery life.

The owner's manual (check reference docs section on the forum) has longevity tips. The two that should give the best 'bang for the buck' are charging to 80% if it works for the trip, and not going to full throttle each time the light turns green.
 
AndyH said:
Nissan only allows us to use 80-84% of total capacity
Click to expand...
AndyH said:
The two that should give the best 'bang for the buck' are charging to 80% if it works for the trip
Click to expand...

I am confused. Are these 80% is a share of predefined 80-84% by Nissan (that is 4/5 * 4/5 = 16/25 = 64% of real battery capacity)?


AndyH said:
and not going to full throttle each time the light turns green.
Click to expand...

Basically it is what ECO mode is enforcing to do.
 
No, at full travel you get full throttle in both modes. ECO mode is just more non-linear to make the first part of the travel much more gentle in acceleration.


jason98 said:
Basically it is what ECO mode is enforcing to do.
Click to expand...
 
jason98 said:
AndyH said:
Nissan only allows us to use 80-84% of total capacity
Click to expand...
AndyH said:
The two that should give the best 'bang for the buck' are charging to 80% if it works for the trip
Click to expand...
I am confused. Are these 80% is a share of predefined 80-84% by Nissan (that is 4/5 * 4/5 = 16/25 = 64% of real battery capacity)?
Click to expand...
That's right, though it might be more like 0.84 * 0.8 = 67%. I'd say, in round numbers, that if you charge to 100% (usable) you are actually using about 5/6 of the battery's capacity, but if you charge to 80% you are using about 2/3.

Ray
 
jlaw99 said:
AndyH said:
Nissan only allows us to use 80-84% of total capacity.
Click to expand...

What does this mean, specifically? Thanks.
Click to expand...
Every cell type has a maximum voltage range. For LiFePO4, it runs from zero to about 4.3V. We know that discharging to zero kills the cell fairly quickly, while continually charging to 4.3 or more kills it a bit more slowly. Most manufacturers recommend that minimum voltage stay above 2.0-2.5V and max stay below 3.6-3.8V. Restricting the upper and lower voltage also keeps us from using the top and bottom capacity.

It looks a bit like this for LiFePO4:

cc_cv_percent_1.jpg


Lithium cobalt (laptop, MP3 player, and Tesla cells) and LiMn is similar, though they normally keep voltages a bit higher - 3.0 'user minimum' and 4.2V 'user max'.

The Leaf's battery management system keeps us between 3.2V and 4.2V - it won't let us 'color' outside the long-life battery charge/discharge zone.

BMSfunction.jpg


Based on a Department of Energy model for the Leaf, it appears that the 'consumer' zone for the Leaf isn't the 80% in the middle - from 10% to 90%, but is likely to be from about 15% to 95% ultimate.
http://www.mynissanleaf.com/viewtopic.php?f=8&t=2464

Here's a great 80% thread:
http://www.mynissanleaf.com/viewtopic.php?f=9&t=2265
 
AndyH said:
Based on a Department of Energy model for the Leaf, it appears that the 'consumer' zone for the Leaf isn't the 80% in the middle - from 10% to 90%, but is likely to be from about 15% to 95% ultimate.
http://www.mynissanleaf.com/viewtopic.php?f=8&t=2464
Click to expand...

Thanks for that post, I ignored that study but it has that fascinating model on battery life.. very interesting reading. Apparently the low end is well protected, so just limiting the charge to 80% will do the job for extending the life.. and air condition your garage if you live in Phoenix.
 
so can we say...

In a nutshell 100% charging presents minimal risk due to the built-in limitations of the charger on the SOC range but 80% is better since the Li has best life in a narrow, but inconvenient middle SOC range?
 
AndyH said:
The owner's manual (check reference docs section on the forum) has longevity tips. The two that should give the best 'bang for the buck' are charging to 80% if it works for the trip, and not going to full throttle each time the light turns green.
Click to expand...
Living in a hilly area will add some stress due to the extra power needed to climb hills, particularly those with steeper grades, you know, the ones that require the use of "power" mode in the Prius. Given that I live in the mountains, I am hoping that this will not be too big a deal. It should help that the LEAF has a relatively large battery pack and can thereby distribute the discharge load. It should also help that most of our roads have reasonable, not overly steep grades, and that one can get away with driving no faster than 40 or 45 mph here. Our cooler weather should also be helpful for battery life. However, there is still an element of uncertainty as to battery capacity loss. To be a pioneer, you have to be willing to assume some risk (or spend more money leasing).

What I will say is that I would not recommend purchasing a LEAF for day-to-day commuting at higher speeds (i.e., 65mph) up and down large mountain grades. Examples would be I-70 west of Denver, I-5 over the Grapevine north of Los Angeles, and I-15 over Cajon Pass from the Los Angeles area to the high desert and Las Vegas. While it may turn out that the LEAF can satisfactorily handle such drives on a regular basis, I would not want to take that chance just yet.
 

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