Joining the 80% Club

[AndyH]

I'll give this my best, George, and will try to provide references and limits.

I've read through this whole thread and I see some folks stating some things as facts and others refuting them with an equal tone of certainty. I've been involved in technical diving forums so I'm somewhat used to having to sort through it on my own and I assume that even the best minds will differ and even evolve their thinking over time, sometimes coming to the opposite conclusion.

Questions for any of you battery Gurus (folks who actually work with this type of battery in other applications or have some level of authority on the subject):

1. Are any of you certain the leaf only allows access to 80% of it's capacity and if so do you have a sense of how much a difference charging to 80% vs 100% of the allowed 80% capacity will make over, say 10 years?

Based on the upper and lower voltage range printed in the Leaf service manual - the voltage limits when if crossed the car stops and stays in a 'no drive/no charge' error mode, and the basic information provided by AESC on the battery used in the Leaf, I'm very confident that we are allowed to use at most about 84% of the maximum available. So our 100% is less than the battery's 100%, and our empty is above the battery's minimum charge.

The LiNiMn cell used in the Leaf has a charge/discharge curve most similar in the lithium family to the traditional lithium cobalt cell phones and laptops. This means that more power is stored in the upper 1/2 of the charge than in the bottom 1/2. Because of this, battery management decisions tend to 'slide' toward the higher cell voltage area of the charge/discharge curve. In other words, instead of using the 80% of the energy between 10% and 90%, they might choose to use the 80% between 15% and 95%. If that's what Nissan did with the Leaf, the it's pretty probable they did, then there might be some benefit to only charging to 80% if that works for us - it may provide a few more miles of travel over the life of the car. (But probably not much more than charging to a mythical 95% consumer.)

But battery management decisions are where the Leaf and cell phone diverge. Portable electronics batteries are limited by size and weight (packaging over cell life) and designed to work very hard until a battery failure gets one back into the phone store. The Leaf is using a large pack with sophisticated management, and the battery is being used and charge at pretty conservative rates - otherwise the pack will not deliver a good lifespan - and Nissan will go broke replacing all those batteries under warranty. Different expected battery experience due to very different design and implementation decisions.

Without knowing any more details of the battery and the car's software, I have no way of knowing how much if any life extension we might see if we only charge to 80% consumer.

2. If no one is certain that 100% of allowed capacity is 80% of actual, how much capacity are we likely to loose over, say 10 years if we charge to 100% as much as possible.

We absolutely are not using the full 100% of the battery capacity. Here are two examples why from the lithium world. First is a look at LiCo state of charge when charged to different end of charge voltages. http://www.powerstream.com/lithuim-ion-charge-voltage.htm

[Numbers on the charge are end of charge voltage - .06 (Ah) is a full cell.]

We can see that we need to charge the cells to about 4.2V to get the rated energy from the cell. But we don't want to end the charge at too high a voltage as even when we only use 80% of total capacity, it'll still greatly affect cycle life.

This info is a look at LiCo battery cycle life. Testing was performed under controlled lab conditions, and only 80% of depth of discharge was used.

at 4.1 volts, you get over 2000 cycles.
at 4.2 volts, you get roughly 500 cycles.
at 4.3 volts, you get under 100 cycles.
at 4.4 volts, you get less than 5 cycles.

A tenth of a volt makes a LOT of difference when we're in the 100-105% SOC range, but much less of a difference in cell life when we drop to or below 4.1V (about 92% of total capacity).

(Leaf cell voltages are a bit higher than plain LiCo so our 4.2V upper limit to trigger an overcharge error is probably closer to LiCo's 4.09-4.1V range with regards to a relative cycle life guestimate...)

2. Is it valuable to run the battery all the way down every once in a while and then recharge to 100% (or in actual terms down to aprox 15 and up to 80-84% raw capacity)?

Not for the battery - lithium doesn't have a memory effect - but it could be very useful to help reset or resynchronize the battery management system and the fuel gauge. The increasing error between 'true state of charge' and 'indicated state of charge' is a known problem in the computer industry (I'm an A+ certified computer tech) but it's not yet been seen in the Leaf. It's a definite maybe.

3. The best battery longevity I've gotten out of cell phones, shavers and lap tops is to charge them frequently, leaving them plugged in nearly all the time, relying on the upper end of the charge capacity and very infrequently draining them all the way down (once a month or so) and immediately charging them back up and leaving them charging for prolonged periods (not sure if there is any true trickle charging going on with the leaf charging system options after max charge is reached). Is it worth using this with my Leaf?

Erase all this data from the past when working with the Leaf. Lithium does not like to be constantly charged. Leaving devices connected to mains power might do nothing - if they have smart management electronics that completely stops charging when the battery is full - or might destroy the cells in short order if they don't have more sophisticated electronics.

There are a lot of things involved in this answer... First, the Leaf has a sophisticated management system, so leaving it plugged in 24/7 is not a problem - the car will stop charging when it chooses. It appears it will also allow some new energy in if necessary after charging is complete. If all other environmental and energy demand variables are controlled, a lithium battery should have a bit longer life if it's not completely charged regularly and not completely discharged every cycle. It's fairly minor though especially compared with the cycle life differences noted above for overvoltage. Using cycle numbers from the above data, maybe we'd get more than 2000 cycles if we further restrict depth of discharge and end of charge voltage, but it's really getting into diminishing returns territory...

4. Is using the L1 charger that comes with the car better than L2, enough to favor it's use whenever possible? I've read that the L2 charger is more sophisticated and better and Nissan recommends using L1 sparingly... not sure what that is based on, maybe just that charging frequently should be done with a hard wired connection rather than a standard plug to reduce chance of corrosion resistance/fire risk.

As far as L1 VS L2 from a car and/or battery perspective, both use the same charger and same control electronics - so neither is necessarily 'safer' for the battery. In addition, both charge rates are very slow. Off the top of my head (it's in other posts but I cannot find them...) L1 is about 4A into the battery and L2 is about 9A. A 1C charge rate is 60A. Very very low impact for either L1 or L2.

5. it's tempting to not want to baby the batteries too much and have them die shortly after the warranty runs out vs before... then again, I'm guessing the warranty will only cover failed cells and not a total cluster replacement.

The warranty seems to make clear that capacity isn't covered. Pack failure should be though - 1 cell or all 192.

While anything's possible, it's highly improbable that one would have massive cell failure around the end of warranty. And the car is already designed around 'babying' the pack - there's not much we can do that would be outside the battery's comfort zone.

I have a 21 cell lithium pack in my motorcycle. The battery has been used all its 3 year life as a test bed for different battery management devices - and for data collection when no battery management installed. In other words, it's been abused from day one. I've replaced a single cell that was damaged by a severe discharge and cell voltage reversal when not protected by a BMS. The other cells, even though each has suffered some level of abuse are just slowly losing capacity at slightly different rates.

To use a tire metaphor to describe my expectations for battery capacity loss, think slow leak, not blowout.

I hope that's useful George.

 

[LEAFfan]

The warranty seems to make clear that capacity isn't covered.quote]

Loss of capacity IS covered if it isn't a gradual loss. The warranty quote in part is: "gradual loss of capacity isn't covered."

 

[AndyH]

The warranty seems to make clear that capacity isn't covered.

Loss of capacity IS covered if it isn't a gradual loss. The warranty quote in part is: "gradual loss of capacity isn't covered."

Maybe. Nissan specifically states that gradual loss is not covered, but doesn't say what IS covered.

Lithium-Ion Battery Gradual Capacity Loss:
The Lithium-ion battery (EV battery), like all lithium-ion batteries, will experience gradual capacity loss with time and use. Loss of battery capacity due to or resulting from gradual capacity loss is NOT covered under the Nissan New Vehicle Limited Warranty.

We can assume (and expect) that any cell failure or significant loss of capacity will be covered (like 191 cells at 29Ah and one cell at 15Ah), but I haven't seen that in writing...

 

[planet4ever]

The warranty seems to make clear that capacity isn't covered.

Loss of capacity IS covered if it isn't a gradual loss. The warranty quote in part is: "gradual loss of capacity isn't covered."

Warranties are written by lawyers. Lawyers use English very precisely. So what is the opposite of "gradual"? Perhaps "rapid"? No, I'm afraid not. The opposite of "gradual" is "abrupt" or "sudden".

Sorry, I'm afraid there is no coverage even for rapid loss of battery capacity. (Besides, rapid and slow are very slippery terms, nearly impossible to defend in a court of law.)

Ray

 

[Stoaty]

Sorry, I'm afraid there is no coverage even for rapid loss of battery capacity. (Besides, rapid and slow are very slippery terms, nearly impossible to defend in a court of law.)

Perhaps, but if word got out that Nissan denied warranty coverage for a case of rapid loss of battery capacity (say a 30-40% loss in 2 years), they would have trouble selling more Leafs. I think the vagueness gives them wiggle room, but if they don't apply a "reasonable person" standard to individual cases they are going to end up killing the Leaf.

 

[AndyH]

Sorry, I'm afraid there is no coverage even for rapid loss of battery capacity. (Besides, rapid and slow are very slippery terms, nearly impossible to defend in a court of law.)

Perhaps, but if word got out that Nissan denied warranty coverage for a case of rapid loss of battery capacity (say a 30-40% loss in 2 years), they would have trouble selling more Leafs. I think the vagueness gives them wiggle room, but if they don't apply a "reasonable person" standard to individual cases they are going to end up killing the Leaf.

That's probably why manufacturers have their 'customer satisfaction warranty' for those that are firm.

We can expect gradual capacity loss - that's the nature of rechargeable cells. But if some of the cells show significant changes, I'd certainly 'strongly suggest' to the dealer that these failing cells should be replaced due to the apparent 'defects in materials...'

 

[Coffee_Slurry]

My own experience with Lithium-Polymer is primarily cellphones (dozens of them), laptops (fewer), and radio-controlled cars, planes, and helicopters (100 cells or so)

Assuming proper management and within-spec usage, the single biggest influence on overall useable lifespan of the battery is ---- manufacturing quality.
A good name-brand cell will deliver peak performance for longer than a cheapo cell.

My cheap cells tend to get out of balance sooner, and generally deteriorate after as little as a year. I still buy them! Dollar-for-dollar, the cheap HongKong batteries are still better performers, even with the reduced expectations. They're just more -- random. Some die soon, some live a long time, but they're just unpredictable.

Most chargers have a "Storage mode" where the cell is brought to 50-70% capacity for longer-term storage. I haven't found any ill effects from two to three months of storage between discharge/charge cycles. I've shelved batteries at 100% charge for months and also not found any reduction. I could be wrong.

The shortest-lived batteries have been those in laptops that stay plugged into A/C. It seems the batteries are shot within a few months. I don't know if it's the higher ambient temperature of a running laptop, the constant 100% SOC, or poor battery management, but this seems to be a given.

I've had Motorola Radio batteries sit "dead dead dead" at sub-volt levels only to take a charge a year later and still deliver 80% of their rated capacity. Sure, they're not peak performers, but hey, they're not trashed either.


So really I have to think that most of the battery life we're going to experience depends on the Nissan manufacturing quality, battery design, and BMS design. The difference between 80% charging and 100% charging every day may take years and years to manifest, or it may be totally overshadowed by the daily demand on the battery, ambient temperatures, or unit-to-unit variation. I'm really curious to see.

Also, at some point, someone is going to get their hands on a bare Nissan battery cell. Hopefully they have the equipment and knowledge to characterize it and share the information in a journal or forum.

 

[GaslessInSeattle]

I'll give this my best, George, and will try to provide references and limits.

....

To use a tire metaphor to describe my expectations for battery capacity loss, think slow leak, not blowout.

I hope that's useful George.

AndyH, thanks for your thoughtful post! we are back from our trip and excited to be driving!

The more I drive this car, the more I only want to drive this car. I'm feeling pretty comfortable that given the fast discharge of use vs the slow charge of L1, I really am best to keep it plugged in and up to 100% whenever possible at least until the L2 gets installed.

g

 

[GaslessInSeattle]

Just got off the phone with someone in telematics from the hotline. I was called a week ago and asked how things were going and mentioned the whole 80% issue and asked if Nissan could clarify why they recommend 80% vs 100%. The person I talked to said she would research the reason and get back to me. They did get back to me and we talked today. They mentioned that the primary reason for the recommendation was convenience and the other issue was that charging the last 20% of the battery generates more heat during charging and heat is one of the main things that is correlated to premature loss of battery capacity.

I asked her if charging with the L1 would be better when charging to 100% because it is slower and presumably would create less heat during the last 20% of charging. She said she couldn't be sure but that that made sense.

So, any of you battery gurus, does my conclusion that charging to 100% is better done on a slower charger, preferring L1 when convenient and avoiding L3 to 100% completely?
g

 

[smkettner]

I joined the 80% club last night. I only have L1. Timer set 12a to 7a so I will get up to 7 hours charging. I am not sure I got fully to 80% but it was certainly close if I didn't. I did notice the night before going to 100% the battery temp was up one notch in the morning and today(80%) it was not. If heat is the primary issue of avoiding 100% it would seem to be a bigger issue in a hot climate.

I could even see going to 100% in a cold climate to get some heat into the battery.

 

[GaslessInSeattle]

I'm still charging on the L1, waiting to hear back from the EV project to see if I qualify for the free L2. So far, just charging when I can, I only reach 100% when charging overnight, meaning I can charge whenever I want during the day without maxing out the battery, effectively cutting down on the number of max cycles. I guess we are sort of part of the 80% by accident. Not sure how this will factor in over time in terms of battery degradation, just thought I'd pass the observation along. We seem to bounce around somewhere between 35mi and 75 mile range during the day. I find these mini charges necessary to keep the battery charged enough to then get a full charge overnight. In fact, the mini charges during the day are motivated by the desire to have a full charge in the morning on the L1 just in case I need full capacity during the day. My wife and I have put most of our miles that we used to put on two vehicles on one our leaf, which is causing the miles to rack up fast. We both work from home and end up tag teaming the car with errands and outings, it's working out surprisingly well!

g

 

[davewill]

...meaning I can charge whenever I want during the day without maxing out the battery...

The only thing I'd watch with all the opportunity charging is letting it get down below 80% before charging. There hasn't been much talk about it on here, but the owner's manual does say not to recharge unless you run it down below 80%.

NISSAN recommends you use the following
driving and charging habits, where possible, to
help maximize the battery’s useful life:
...
Allow the battery charge to be below at least
80% before charging.
...

So, if you do short errands that don't run it down much, you might not want to plug it in.

 

[edatoakrun]

I'm in the club, and very happy with the range that put me there. I had questioned the range effect of a fairly significant descent and climb, and whether 80% would work for me. I Hope the info below will give some other hill dwellers an idea of what to expect. In my experience, brake regen gives a large fraction of descent energy back. This is very good news for me, as there are flat roads only in one direction from my home, west toward the Anderson Valley (and the central valley further south).

My variable 50-60 mile Drive to Redding, CA includes over 2,000 ft of descent, about 1500 net down to the valley floor.

I timer charged to 80%, showing 10 bars and 54 mile range.

During the first 7 miles with most of the descent, the range estimate increased to 100 miles. I hadn't expected regen to put on another bar, and it didn't. The drive was fairly flat the next 40 miles, average speed about 50 mph, 1/3 freeway, 2/3 town and county roads.

At 14 miles I lost the tenth bar.

At 17 miles, I parked, and lost the ninth bar when I restarted.

Lost 8th to 4th bars at expected intervals over 47 miles (including the about 12 miles of freeway) by which time I was back into the final 6 mile climb home.

3rd bar went at 51.

Still had 2 bars and 11 miles range when I got home at 52 miles. I'm L2 charging on a Kill-a-watt, and will report when I get the total for an 80% recharge. (edit-it took 14.77 kWh)

Yes, I took it easy, and the trip took 5-10 minutes longer than in any car I have owned, but no longer than my F250 or Cherokee. The LEAF handles quite well, and it was enjoyable picking up time on the mountain roads, that I lost driving 55-58 on the freeway. Next trip I'll increase the speed, now that I'm cured of RA.

IMO, the LEAF meets all range predictions made by Nissan.

I agree that it's a milestone car, as the first mass-market BEV, and deserving of the award of world car of the year.

 

[GaslessInSeattle]

...meaning I can charge whenever I want during the day without maxing out the battery...

The only thing I'd watch with all the opportunity charging is letting it get down below 80% before charging. There hasn't been much talk about it on here, but the owner's manual does say not to recharge unless you run it down below 80%.

NISSAN recommends you use the following
driving and charging habits, where possible, to
help maximize the battery’s useful life:
...
Allow the battery charge to be below at least
80% before charging.
...

So, if you do short errands that don't run it down much, you might not want to plug it in.

thanks for the reminder Dave. Maybe I made it sound like it's always plugged in when in reality I'm not being that persistent.
g

 

[GaslessInSeattle]

while trying to fix my Carwings, I came across this article on "Depth of Discharge" and thought I'd pass it along. Seems Nissan allows one to access about 75% of the actual battery capacity.

http://nissan-leaf.net/2010/08/04/leaf-depth-of-discharge/

g

 

[TomT]

That's one person's opinion and not really based on any hard evidence. I'd take it with a big grain of salt... There is a lot of contradictory information right here on MNL...

while trying to fix my Carwings, I came across this article on "Depth of Discharge" and thought I'd pass it along. Seems Nissan allows one to access about 75% of the actual battery capacity.

http://nissan-leaf.net/2010/08/04/leaf-depth-of-discharge/

g

 

[evnow]

I'm now mostly charging 80% - even on weekends. That has been good enough.

Having leased the car - my main problem is that I don't like the brake feeling without regen. On 100% charge I get no regen while descending to the "valley". So, my timers are now set to 80% even on weekend. I manually start charging to 100% if need be.

ps : valley is in quotes because it is too narrow. Seattle area geography is carved by the last ice age - with the main glacier route now used for I-90

 

[GaslessInSeattle]

the more I look into this whole battery capacity issue the more I wonder "What does the battery warranty really cover? ie, how hard should I worry about extending the life of the battery? At first it seemed like splitting hairs, now I'm pretty convinced it's a big enough deal to pay close attention to.

From what I’ve gathered to date, the reasons for taking special care of the battery are becoming compelling (more than a matter of a few % over 10 years), as it appears we may have the ability to charge the battery to 100% of the battery’s actual capacity, enough to abuse it and substantially shorten it’s life. From what I can tell there is essentially no level of degradation that Nissan explicitly considers “beyond normal use”. In other words whatever degradation occurs over time, there is no indication that it will be covered under warranty, no matter how steep the decline. This makes me willing put some effort into creating optimal charging/discharging habits so as to preserve the car's resale value and avoid having to purchase a new battery prematurely. Below is how I have come to this.

I’ve read article on Li-Ion Battery Life that’s been circulating: http://powerelectronics.com/portabl...y_charger_ics/804PET22li-ion-battery-life.pdf

The article does a good job of explaining why avoiding the upper and lower end of a Li-ion battery’s charging capacity could substantially improve it’s life, as in roughly double it. It’s hard to know how relevant the article is to the Leaf's large and complex battery bank.

I’ve also done my best to get a handle on how much of the charging capacity of the Leaf’s battery we even have access to. We would hope it has one of the best battery management systems on the planet. The most convincing post I've read so far is Bill’s, which can be found here: http://www.mynissanleaf.com/viewtopic.php?f=26&t=1401&start=150 He does a decent job of explaining how he believes we are given the ability to charge the battery to it's actual 100% and using the upper 20% could accelerate eating up the cycle life of the battery by 1.6 times per max charge.

I’ve also read through some of the information put out by Nissan to try and look for clues about how to quantify all this. On my quest for more hard numbers I noticed I’d overlooked something in the Owners manual.

From Page 3, beginning with the usual disclaimer that under normal use and function, a Li-ion battery's charge capacity decreases with time and usage. About three quarters of the way down the paragraph I see something I have not noticed before: "Nissan estimates that the battery capacity will be approximately 80% of original capacity after five years, although this is only an estimate, and this percentage may vary ( and could be significantly lower) depending on individual vehicle and Li-ion battery usage."

I thought it was something like a 10- 20% over ten years, not five and saying it depends on the vehicle and not just usage, suggest they assume some vehicles are manufactured better than others. To read it's expected to be 20% or worse over 5 years does give me pause. To me, the above paragraph leaves wide open the degree to which Nissan will ever attribute capacity loss to a warrantable issue. It appears to me that Nissan is not willing to put in writing what constitutes a warrantable battery failure. All of this, even if the vehicle is used as designed. To say the car has a 100 mile range and then essentially state that relying on that range with regularity could substantially reduce the car's capacity over time does seem to be a bit disingenuous. That said, I still love the car!

What I’ve decided to do as a result:

I was considering using the L1 charger as my primary, but have now decided against it given the usage and charging time patterns over the first 1,000 miles. I’ve concluded it’s not generally feasible to charge the car fast enough on the slow charger to meet our spontaneous lifestyle when only charging to 80% overnight and opportunity charging during the day. This has substantially increased my motivation to get the L2 charger installed STAT, which is now underway.

The good news is that it appears that using the L2 charger will substantially improve the feasibility of 80% charging. I guess you could say that I am coming around to the conclusion that the manufacturers’ recommendations are worth sticking to ie, using the L2 charger primarily and only charging to 80%. Doing this should stand to give us functional, relatively carefree use of the vehicle and a decent battery life. From what I’ve read, frequent mini charges in the middle 50% of the battery does the least to degrade the battery over time and only count for a small % of a typical full charging cycle in terms of cycle life. The L2 should be fast enough to allow for the short “top off’s” during the day that we’ll need to do between outings to avoid the turtle. I still plan on taking the car on longish trips on occasion and maxing out it’s capacity, I just don’t plan on doing this with any kind of regularity and I now have a much better sense of what's it will cost me.

Unless I can find reason to believe otherwise, it’s looking like I’m going to be a fairly devoted 80% club member once the L2 is up and running!

g

 

[Coffee_Slurry]

My typical range is around 65 miles, with a lot of fast freeway mixed in.
Charging to 80% means I get only 52 miles of range. That's a lot of mileage to leave on the table.

My car will be a test case for three years of daily 100% charging.

IMHO, the whole L1 (1.4kW) vs L2 (3.3kW) thing is totally overblown. As far as the car is concerned, they're both trickles. I wouldn't think the charge rate makes any difference until you get up to 1C, which would be a 24kW charger, or at least 0.5C (12kW). Our L2 charger is a long way south of that, and just doesn't heat up the batteries much at all.

 

[GaslessInSeattle]

...

IMHO, the whole L1 (1.4kW) vs L2 (3.3kW) thing is totally overblown. As far as the car is concerned, they're both trickles. I wouldn't think the charge rate makes any difference until you get up to 1C, which would be a 24kW charger, or at least 0.5C (12kW). Our L2 charger is a long way south of that, and just doesn't heat up the batteries much at all.

That has been my conclusion as well, however for those who rent or are not sure if they are staying putt or just wanting to save some money, the included L1 charger has it's temptations beyond any notion of extending battery life.

g