Saturday, October 21, 2017

If You Have Battery Degradation, Read This!

Every day, I read posts from people who have lost a capacity bar on their LEAF and seeking information on why it happened or if their car is normal or not.  EVERY ONE of these posts do not provide the information that is needed to make a decent evaluation of that person's situation.

The reality is we as a society don't have the faintest clue as to what to do to maintain our battery packs. What I see is "I babied my pack and still lost a bar" which would imply they knew exactly what to do and guess what?? They were wrong.

What we need is a reference guide as to what we need to consider and more importantly a checklist as to what we need to report when looking for advice online!


Now this chart represents general guidelines on what affects the general rate of degradation. It is not a chart in reality. Only a visual representation only. What does "not a chart mean?" What it means is that X,Y points are not observed data points so should not be referenced.  The important takeaway here is the meaning of each color and its relationship to other colors on the chart. Despite SOC and temperatures being the most important aspect of the chart, they are for relational reference only (hotter/colder,  High SOC/ Low SOC)    

Now, we all know Nissan put the fear of God into us when charging to 100% and letting it sit. They even went so far as to put in an 80% charge option for a few years. Thankfully, they quickly realized that the wrong message was received and removed the 80% charge.   So lets look at the 100% SOC area.  First thing we see is that there is some Red when the temperature gets hot enough but we have to be on "Broil" (or live in Phoenix) to see Black.  Luckily, even Nissan knows this so they restricted the charge to 97% so the downside of charging to full overnight is pretty minimal. What Nissan did do is allow you to manipulate the charge so it finishes near the time you would be leaving so again, no real downside to charging to full!  Now this chart does not input any time parameters in here so that is on us to guess but in Winter, there is little reason to not charge to full every day.

So the next question becomes "Why are you not recommending I stay in the Yellow ALL THE TIME?"  Well, I am recommending that you do... IF you can. Realize staying in the yellow means your already limited EV range is now cut by MORE than half.   Another reason and much more important is look at the cushion you have between the Yellow and the Red at the bottom verses the cushion at the top?   Not a lot of forgiveness is there?

Thanks to the GOM's subliminal hypnotic suggestion, we tend to think we have more range than we really do. We also underestimate the impact of our habits like heat, taking the wrong route to work, etc.  After all, at the end of the day, how many times to do say "Wow, look at all that extra range!"
So, lets pretend "Yellow" doesn't exist.  For those of you that are retired, work at home or simply have nowhere to go, good for you! Your LEAF will last you a lifetime but then again you don't post online about losing bars anyway so the next time someone asks why Nissan removed the 80% option, now you know.

Now, I do have one recommendation; In Summer, if your ONE WAY commute does not drop your SOC below 80%, then probably shouldn't charge to full unless you are in an underground parking thingy, middle of the forest  or some place with a lot of shade.

Another thing to look at is the huge number of people who charge at work. The chart above shows Red in the mid 80's for SOCs at 80% (remember X,Y points are not valid so its important to understand the hotter the worse)  so if you are going to do this make sure you have shade and you don't start charging until after lunch. Remember, your packs can see radiant heat well over 100º on the mildest of Sunny days (People who live in San Diego or any other Sunny coastal area, please take notice. Your weather is FAR from perfect) So 80% would have been perfect for this right?  No, not really.  What it would do is give people the false impression that 80% would be ok even if done by lunch. In a perfect World, we would hit 80% 5 mins before 5.  The reality is half of you probably charge in the morning while your co-workers charge in the afternoon. Who is going to volunteer to be a "Red" EV?

Ok, so the full charge question is out of the way, lets look at the MUCH more familiar low SOC.

One of the things Nissan has not removed is the low state of charge warnings and for good reason. Look at the chart; other than extreme heat, low SOC is BY FAR THE NUMBER ONE reason for degradation. Remember this because this is THE MOST CRITICAL PART of the survey.  Low SOC is not affected in anyway by temperature which means this applies to everyone no matter where you live.  Simply another reason why you should charge more than you think you need. Its simply a good idea.

But I constantly read how people made it home with 8 GIDs and were proud of themselves and I ask them if they plugged in the car and they say, "I am fine, its on a timer"  or they say "I only charge when the rates aren't 30 cents per kwh"  and I think "Why do they want to screw themselves over like that??"  Is saving 50 cents really that important to you that you would sacrifice a $5500 battery pack? What is wrong with you!!

Either way; My recommendation on this is if you get home with ANY battery warning on, plug in ASAP. This is what I do and its only for 60-90 mins. Sometimes 2 hours if  I spaced it off.   How important is this recommendation?  It is the MOST important thing this blog is relaying to anyone.  Couple things to consider; The LBW (low battery warning) comes on first and it comes on at 16% more or less. Well, look at the chart. The Red starts at 25ish % SOC. So by the time you see that warning, you are already beating up on the pack...

Ok so the basics of charging are out of the way, so now we need to get into the checklist for info you want to provide us online to get insight into your degradation issues.

**Location. This is important to evaluate your climate

**Build date (located on driver door jamb) Purchase date and any info about time spent on the lot.  Dates are also important because there is a huge difference between spending ONE month on the lot in Summer verses Winter.

**Driving habits. How far you drive,  how fast (be specific. "keeping up with traffic" is not an answer)   mostly freeway? Cold blooded (run heat at 80º on a 65º day?... Don't laugh, I know a lot of people who do EXACTLY this!) Hypermiler or constantly late?

**Efficiency. What is your miles per kwh average? Its on your display and can be reset as often as you deem necessary and I highly recommend you do it often. At least on every season change. I reset mine DAILY.

**Charging habits.  Do you plug in ASAP at low SOC? (anything under 25 miles on the GOM)  What is charging type and speed?  Charge to full every day or only a few times a week? Charge at work?  Fast charge?  There is no such thing as too much info here.

**Parking habits. Garage or driveway.  At work; Garage? Park in shade whenever possible and is it possible? Get to work with less than 80% SOC and more than 30% SOC

Finally the thing to keep in mind is the above info is the MINIMUM you should provide and when if you forget something, no worries but adding that info in the middle of a 100 post thread... well you might as well not add it at all. Any question answered in the thread should be updated on the your original post.  Your original post, nearly everyone will get 75% of the info contained in it. As for additional info added in the thread of the post? You lucky if 10% see it.

Remember that this battery babysitting thing is still a bit new to all of us and we are still learning just like you but the quality of what we know is solely dependent on the quality of the information we receive and the thing to remember, we are all doing this to learn how to keep those 12 bars as long as possible so everything we learn from you will benefit everyone!

18 comments:

  1. This is helpful, but I'd like to know where the graph came from. Is it yours? Borrowed? What were the model assumptions? I am disagreeing with you, but the blog post is premised on the validity of the graph, and you don't provide that.

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    1. Don't know where graph came from. I swiped it from someone somewhere a few years back. I think it was from facebook. I have done a few Google searches but have not found nothing. There are however several battery sites that provide the same info by context. Just don't provide a good graphical representation. I am sure there is a graph out there that is similar and one day I will find it

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    2. The C/F scale on the graph is wrong.30 degrees C is 86 degrees F. So - which is right?

      This does not add or subject from your main point - thanks for the info.

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    3. Ok, I went back and bolded the key statement about the chart. This is simply a visual representation of how different actions affect degradation. Its on a graph with labeled axis and yeah, that gives the impression that any X, Y coordinate is observed and this is not the case here. We also need to keep in mind this chart IS NOT LEAF specific. Its only for general Li Ion chemistry. There are several and each has its unique characteristic that will move the lines of this graph around but the shape and general relationship of the colors on this graph are essentially true for all Li Ion chemistry.

      The whole point of this blog is to advise that heat is not the only thing we need to consider. There are other things like low SOC that can be addressed and in many cases, VERY easily. Too many people I talk to ONLY base their charging on TOU and I believe this to be an error. How much of an error? Dont know but this chart indicates its a mistake.

      Now the ONE thing we can't do is assume that point XX a red area 1 block away from Green is twice as good as point YY that is also red but two blocks from the green. XX is better but to what degree, we don't know. It could be insignificant or simply more time based than situational based.

      For more info, check my next blog entry

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  2. The chart is evidence enough that EV's with no active cooling system should be sold only in moderate climates. In warmer climates its simply too inconvenient to operate within the small area shown on the chart.

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    1. True that because I wouldn't want to pay it! I don't need it. But I am fairly confident, TMS as an option is coming in 2019 with the 60 kwh packs.

      FYI; on my S30; This morning ahr 82.34, SOH 100%, HX 100% GIDs 363 AND 25,000 miles. So I am sure if I let the car sit enough, the numbers will dip but pack is still holding up. Build date 10/16

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  3. If there is a “reserve” of 10% that is unusable (Net vs gross kWh pack rating), then the low battery warning at 16% is actually 26%, right? Then plugging in as close as possible to the warning isn’t really that bad, according to your graph, which I’m guessing is showing gross SOC not net SOC.

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  4. We need to remember that is technically "not" a graph. It is only a visual representation of what causes degradation. So the number where you see the line is NOT A DATA POINT. It simply is in pictorial format in order to be quickly understood.

    The other thing is this chart is not LEAF specific. Its only a general guideline for Li batteries lacking TMS.

    the warning comes on at 48-50 GIDs which was just over 16% on 24kwh packs. On 30 kwh packs it comes on at the same GID so it would be less than 16% but that is real capacity and keep in mind; out of that 16%, not all is usable. There is a few percent that can't be accessed. How much is completely dependent on how well balanced your cells are as the shutdown point will be from the lowest cell hitting the voltage cutoff.

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  5. So you can use all 30 kWh of pack capacity? I know on my e-Golf, there is a ~11% reserve that I am unable to use, based on the indicated efficiency. Say, if you get 5 miles/kWh on local roads in the Leaf, can you really drive 5*30=150 miles? Or is more like 135 miles? If it's more like 130 miles, that would indicate there is capacity that you can't access. So that's why I'm suggesting there is ~10% capacity (in the black zone) that you can never reach. Maybe I'm just confused?

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    1. You can use roughly 93%. The car charges to roughly 97% max and the low end of the usable range boundary is 2-3% and that is voltage controlled so its dependent on how well the cells are balanced. Better balance means a deeper discharge.

      This is one of the LEAF's major problems. Charging too high. the rate of degradation increases quite a bit when SOC is that high and combined with relatively mild temperatures that are likely in the 80's. Just stopping the charge at 93-94% would have helped a ton with degradation in a lot of areas in the country but Nissan in its wisdom felt it should be full or 80%, neither of which was a good idea in a EV that only had no more than 80-85 miles to give.

      Soon the LEAF will have 40 kwh and being able to stop the charge in the low 90's% will go a long way towards making that pack last much longer.

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  7. I thought the justification to eliminate 80% Charging in the LEAF by Nissan was so that they could claim the higher EPA range? I typically don't need the full range,so I continue to charge to 80% unless I need extra miles. My own anecdotal evidence that this helps is comparing my 2011 Nissan LEAF capacity readings (currently 10 bars at 33k miles) with that of a friend's 2011 LEAF who was down 4 bars at 45k miles. Same Climate. Granted there are other variables that could account for his faster loss of bars, but I'll continue to stick to my regular 80% charging approach. I am convinced it does make a difference.

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    1. That is Nissan's claim which is quite nonsensical. I never used the 80% setting when I had it but I live in an optimal climate for the most part although this past Summer was not so good for batteries and heavy fast charging like I did.

      But the reality is 24 kwh ranges are so limited, it was hard to do the 80% for me. Now 40 kwh will be a lot easier to keep in middle to lower SOC range during Summer because of the extra capacity.

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