Optimal Portion of Battery to Use for Longest Battery Life?

[JPWhite]

I don't actually own a LEAF yet, but have been reading to learn all I can. I think by setting an end time on your charge cycle, the car will "time" the charge such that it starts its charge as late as possible. IOW :

1. Say you need a 40% charge to 80% every night based on your commute.
2. The LEAF calculates it takes 2 hours to do so
3. Your end charge time is set to 8AM (no start time needed unless you have TOU)

It will start charging at 6AM thereby leaving the battery at a lower SOC for a longer time. As an engineer, I would do this to ensure longer battery life.

Someone please correct me if I'm wrong.

-Alex

Page nine of the warranty manual says the following about incorrect charging procedure that would void the warranty.

Charging the lithium-ion battery full on a daily basis
despite the lithium-ion battery keeping a high state
of charge level (98-100%).

So topping off from say 50% to 80% during the middle of the day would not be a warranty issue. Not sure what the impact on overall capacity though.

 

[EVDRIVER]

It's clear Nissan does not want the pack sitting at 100% for 50% of the time, an 80% timer solves this issue. Even if charging to 100% has marginal or no adverse impact, if it is done every day it will keep the car sitting at 100% most of the time.

 

[tps]

He also said charging at 120V will shorten the pack life by 27% based on their testing because the cells don't like 120V, only 240 and above.

??? The onboard charger is a switching power supply. It has to up-convert both 120V and 240V to something higher than the pack voltage in order to get current to flow into the pack. So how do the cells know what the incoming voltage to the charger is? The voltage output of the charger may be very slightly lower thus the current flowing into to the pack may be lower when charging from 120V, due to the fact that the power draw of the charger is very much limited at 120V.

Could you expand on why the pack life might be shortened by 120V charging?

 

[TomT]

For those who don't know EVDRIVER that well, he is being facetious... :lol:

I'm visiting the Nissan factory in Japan and I was able to meet with their senior battery engineer Shiro Lithimoto and after speaking with him for more than an hour he told me the 80% charge level was there to protect the pack in high heat climates during equalization and those in temperate climates will not benefit form this mode. He maintains that for the longest pack life one should attempt to discharge the pack no more than 90% and try to use the area between 40% and 50% SOC as little as possible so don't leave it sitting in that range and drive fast when at 50%. to get below 40% quickly. He also said charging at 120V will shorten the pack life by 27% based on their testing because the cells don't like 120V, only 240 and above.

 

[EVDRIVER]

For those who don't know EVDRIVER that well, he is being facetious... :lol:

I'm visiting the Nissan factory in Japan and I was able to meet with their senior battery engineer Shiro Lithimoto and after speaking with him for more than an hour he told me the 80% charge level was there to protect the pack in high heat climates during equalization and those in temperate climates will not benefit form this mode. He maintains that for the longest pack life one should attempt to discharge the pack no more than 90% and try to use the area between 40% and 50% SOC as little as possible so don't leave it sitting in that range and drive fast when at 50%. to get below 40% quickly. He also said charging at 120V will shorten the pack life by 27% based on their testing because the cells don't like 120V, only 240 and above.

Was it his name that gave it away or not using the center of the pack? It'a about as accurate as some of the other posts about pack charging

 

[surfingslovak]

Shiro Lithimoto

:lol:

 

[EVDRIVER]

Shiro Lithimoto

:lol:

That's no BMS.

 

[surfingslovak]

That's no BMS.

Yes, please say 'Hi' to Shagiro Sisakilawato when you see him. Good guy, ask him about his next trip stateside, will you?

 

[ebill3]

OK, I got sucked in. :lol:

 

[Volusiano]

OK, I got sucked in. :lol:

+1

 

[Stoaty]

I think it's really overkill to purposefully not charge the car to 80% right away at first opportunity so that it's always at the "Ready to Go" state as often as possible, just for the sake of MAYBE prolonging the battery life (or maybe not true).

What if you have an emergency situation and need to use it? Even if it's not an emergency, what if you all of a sudden have an unplanned errand you want to run late at night? Like go to a pharmacy for some medicine, or go pick up your kids from a sleepover because they got sick, or run to a Walmart for something you suddenly need, etc?

An urgent errand for me would likely be a 5-7 mile round trip, easily covered by a lower state of charge. In the rare case that I would have an emergency situation, I can use the ICE car. In the last 2 months, this has happened zero times. I expect it could happen as often as 1-2 times per year, thus adding up to 100 miles per year to my ICE vehicle (on top of the 3,000 I expect to put on it for long trips).

In other words, the downside of purposely keeping a lower state of charge is almost none--for me. The chance that it may improve the battery life slightly is worth the small change of habit required. For others, the calculation will likely be different.

 

[Volusiano]

The chance that it may improve the battery life slightly is worth the small change of habit required.

There's also a chance that it won't improve battery life but may degrade battery life instead, by keeping a low SOC most of the times and delay charging until morning. So you may end up hurting the battery instead of helping the battery. We just really don't know unless it's clearly stated otherwise by Nissan.

Let's look at it another way, Nissan for sure has to know or has to assume that most people will want to charge their cars to 80% as soon as they have the first opportunity to do so just so they have a car fully ready at their service. If this is not good for battery longevity, Nissan would have said something about it. They would have advised users that for even better longevity, program your timer using the END timer so the battery is ready only WHEN you need it. But instead, they said nothing of the sort. That would imply that they see nothing wrong with people charging their cars to 80% SOC as soon as possible.

So why fuss over something that probably amounts to nothing? All the while foregoing the advantage of having your car ready at your disposal at 80% SOC all the times.

 

[surfingslovak]

And if I have to guess, I'll roll my dice with 2) because at least I know for sure 2) has a clear and irrefutable advantage over 1): I'll always have 80% of charge ready at my disposal at all time, the way it should be.

Very well put, and I would agree that 2) is the sensible choice here.

It's all speculation at this point, but as Dan Myggen from Tesla said in his eloquent email to a customer: battery degradation is a function of time spent at voltage and temperature. The 80% charge is within the range Nissan recommends and if you drive your Leaf frequently enough, the battery won't spend much time at 80% charge. Long-term storage might require additional considerations, but since Nissan did not come up with a specific storage program, perhaps we don't have to worry about that either.

If you were interested in the specific amount of cell damage caused during a full battery cycle, have a look at Steven Moore's blog entry. He analyzes iPhone 3GS battery management, and tries to quantify cell damage in minute detail. If I understand his chart and the reasoning that goes with it correctly, the amount of damage caused above 80% SOC (left side) is substantially higher than the amount of damage at low SOC (right side).

I think the primary reason for avoiding the lower regions of battery capacity is improved cycle life due to a shallower depth of discharge, and not the specific amount of damage suffered at low SOC. Also, depending on the specific battery discharge characteristic, energy might be more readily available and more predictable at higher SOC than in the lower battery regions.

The usual caveats apply: this is a different cell, different application and a different design. However, the chart may be good enough for educational purposes, that's at least how I'm taking it.



Charged <-------------------------------- Cathode Entropy Curve ------------------------------> Discharged

Battery: Lithium Cobalt from iPhone 3GS
Source: http://stephenwmoore.wordpress.com/2009/07/21/iphone-battery-life/" onclick="window.open(this.href);return false;

 

[Stoaty]

Let's look at it another way, Nissan for sure has to know or has to assume that most people will want to charge their cars to 80% as soon as they have the first opportunity to do so just so they have a car fully ready at their service. If this is not good for battery longevity, Nissan would have said something about it.

I don't think Nissan is giving us any details about optimal care of the battery, because to do so would imply that taking care of an electric car is complicated. That isn't the message they want to convey, and I agree with them for the masses. The recommendations from Tesla are the closest thing to helpful information we are likely to get.

 

[Herm]

I don't think Nissan is giving us any details about optimal care of the battery, because to do so would imply that taking care of an electric car is complicated.

Its a good point, but perhaps just charging to 80% ASAP is all that is really worthwhile (for stretching battery life) to do. I charge my unused lipos to 50% and store them in the fridge, probably overkill.

 

[ericsf]

The recommendations from Tesla are the closest thing to helpful information we are likely to get.

The LEAF's battery chemistry is Li-Ion Manganate. Not Li-Ion Cobalt. The information from Tesla will help us know how to manage cell phone or laptop batteries. Not the LEAF's batteries. It may actually contradict what's best for the LEAF. Personally, I would stay away from those.

http://batteryuniversity.com/learn/article/types_of_lithium_ion

 

[thankyouOB]

I think it's really overkill to purposefully not charge the car to 80% right away at first opportunity so that it's always at the "Ready to Go" state as often as possible, just for the sake of MAYBE prolonging the battery life (or maybe not true).

What if you have an emergency situation and need to use it? Even if it's not an emergency, what if you all of a sudden have an unplanned errand you want to run late at night? Like go to a pharmacy for some medicine, or go pick up your kids from a sleepover because they got sick, or run to a Walmart for something you suddenly need, etc?

An urgent errand for me would likely be a 5-7 mile round trip, easily covered by a lower state of charge. In the rare case that I would have an emergency situation, I can use the ICE car. In the last 2 months, this has happened zero times. I expect it could happen as often as 1-2 times per year, thus adding up to 100 miles per year to my ICE vehicle (on top of the 3,000 I expect to put on it for long trips).

In other words, the downside of purposely keeping a lower state of charge is almost none--for me. The chance that it may improve the battery life slightly is worth the small change of habit required. For others, the calculation will likely be different.

I am with stoaty, as I have the luxury of an ICE on standby. and that it is what it has done every day since I got the Leaf -- stand by.

 

[surfingslovak]

The LEAF's battery chemistry is Li-Ion Manganate. Not Li-Ion Cobalt. The information from Tesla will help us know how to manage cell phone or laptop batteries. Not the LEAF's batteries. It may actually contradict what's best for the LEAF. Personally, I would stay away from those.

That's a very astute observation. However, I've heard that lithium cobalt is the closest cousin of lithium manganese. Obviously, these are different cells, but the application (an EV) is the same and at least some of the recommendations Tesla gives are accurate.

One of the things I've adopted is that I time full charges with the beginning of my trip to make sure that the Leaf does not sit all day fully charged. The second thing I've adopted is not parking the Leaf in the sun, and I put it in an underground garage when I'm at work. And the third thing I've adopted, is keeping the SOC around 50% when I'm only doing short trips. Overkill? Perhaps, but so long Nissan is mum with their information on battery care and does not provide battery capacity warranty, I feel the need to protect my investment.

As Volusiano mentioned in his post, the Leaf is here to serve the owners needs, and not the other way around. I would recommend that as something we should go by, and worry about the battery only if our requirements are met.

 

[TomT]

+1!

The LEAF's battery chemistry is Li-Ion Manganate. Not Li-Ion Cobalt. The information from Tesla will help us know how to manage cell phone or laptop batteries. Not the LEAF's batteries. It may actually contradict what's best for the LEAF. Personally, I would stay away from those.

 

[ericsf]

lithium cobalt is the closest cousin of lithium manganese

Yes, they are the closest but yet different. For instance, Li-Ion Manganate batteries won't explode if you overcharge them. They have about 30% less capacity but can deliver more current. If you follow the link I posted you'll see that the structure of the atoms in the cells is completely different. Cousins, yes but one's a boy and the other's a girl ;-)

I think the differences are very relevant if we're trying determine how to best take care of the battery. When it comes to chemistry, properties of elements are very difficult to "guess". Look at carbon. Could you guess that diamonds and coal are made of the same thing?

Also, if the statement Nissan made that using fast charging once every day would only decrease the battery life 10% faster than normal charge (80% remaining capacity after 7 years) is true then I think that the behavior we're discussing here would have much less impact on the battery. Fast charging seem to be by far what puts stress on the battery.

It will take years - maybe decades until we know how those batteries pass the test of time and miles. Let's meet again in 5 years and see who still has 99% and who's down to 80% and discuss how we used our cars.

I put my money on :
1) Fast charging everyday (not recommanded by Nissan)
2) Leaving the battery idle for long period of time charged at 100% (voids the warranty).
3) Climate (exposure to hight temperature voids the warranty).

Not new information but I think everything else will have non measurable effects on the battery.