Thursday, September 28, 2017

I Choose Degradation!

This statement may come as a bit of a shocker to most EVers since this is the very thing we do our best to avoid and or ignore.  But the reality is Lithium packs degrade starting almost immediately. Granted; proper maintenance, habits and good SW/BMS can slow the process to a crawl but at the same time, after 24,000 miles, the pack is NOT as good as new, period.  Now we could have a Tesla where most would say there has been no degradation at all armed with data showing they have a range of 103% of new or something crazy like that but whether you have so much range, a few miles here or there simply don't matter or it gets lost in the humongous battery pack, it is there.

Now, I could elect to use LEAF Spy data concerning only the SOH (still 100%) or the GIDs (still 363) or the Kwh available at full charge (still 28.1 kwh) That is a majority, 3 out of 5! Majority rules, right! OH YEAH!!

But that would not really make sense or be realistic.  So maybe its time to look at Hx which I have been unable to get over 100% (like why is that even possible?)  for nearly 2 weeks despite doing "all the right stuff" but lets face it; we all know that quick charging and deep cycling the pack several days in a row does not make the pack stronger.  It more likely simply recalibrates the BMS making it more accurate. So you aren't gaining anything, only seeing what you already had.

I do choose my ahr reading which I have always preferred the most after GIDs but we all kinda have a fondness for GIDs simply because its not a Nissan thing, its a EV synergetic community thing.  But it is no longer at 82.34 ahr and unlike the last two times the metric dipped (due to extended rest periods) this time, it is not likely to come back.  In fact, despite driving 60 to 140 miles a day, it has slowly dropped every day. Its now wallowing in the mid 81's.

So the real question becomes what is my level of degradation really?  Ahr say just over 1% which is not likely. Remember, I have baked my pack into the red maybe 10 times, but hit 9 or 10 temperature bars DOZENS of times.  So 1%? Not likely. 

Hx says 3 % (well not quite yet but guessing it will by tomorrow morning) So that might be more plausible but problem with both ahr and Hx is volatility.  Unlike SOH and GIDs that move rather slowly and somewhat predictably,  they are the two numbers that move the most making it difficult to determine exactly where they really are.  I can move them both down 3-4% quite easily by simply taking a 3 day weekend at home on the couch! This was possible back when my pack was still new (and likely undegraded!) so wonder how it far it would drop now if I did it?  Remember, I did the experiment with my LEAF driving it infrequently during the first month of Leasorship. I was able to get the Hx to pretty much where its at now but also had the ahr move to 81.49 ahr on November 29th, 2016. (My delivery date... why do we call it that? I had to go get it, so my "pickup date" was 11/11/16)

Now, I can't really go by remaining range due to too many variables with trips in my area.  I didn't do a real range test back when the LEAF was new other than random observations. Just didn't see the point. It was all about what I could do now that I couldn't do before and in the grand scheme of things, that is the only thing that counts. Now, my 24 kwh LEAF I could do casual range tests easily because one common work destination was 95.8 miles round trip (you don't have to drive it until it dies. That is lunacy anyway. You only need to drive to the point that the error in estimating your remaining range is minimal which is easy to do if you are guessing 2-5 miles)

So for now, I will be going with the 3 % loss. This means I have just about one less kwh available (despite what LEAF Spy says and realize, it ain't LEAF Spy saying it. LEAF Spy is just the messenger and you know the policy about violence against your messenger!) or 3-4 miles less range. I might see range in the high 80's this Winter (had one really nasty day with range in low 90's but that was aggravated by having 4 in the car which really kicked up the defrost need and it wasn't even that cold!)

This brings me to another point in that my 24 kwh LEAF numbers seemed to move more in concert with each other.  Hx and SOH were rarely more than 1-2% apart (good pack balance!) so wondering why the numbers are starting to spread?  I have also noticed this with several other people where their numbers are all over the map including a few with more than 10% differences! Crazy stuff!

But  now I can start a trend line and yeah, its likely to be readjusted but at this pace I will end my lease with 95% Capacity!!!.... if I honor the terms I agreed to of driving it 45,000 miles that is. We'll have to address that later.

Now I thought about waiting another 3-4 days or at least until my ahr and Hx stopped dropping but it getting near the end of the month and I found that putting stuff in the monthly drive report never seems to get noticed plus I have some spare time right now (which is rare but should be more plentiful within the next 6 weeks or so as work winds down for the holidays)  but I may well be back next week in a panic when my LEAF shoots below 95% or something... or not!


  1. Sorry for my ignorance, but what does GID and Hx mean?
    I currently drive a 2015 e-Golf with the lease expiring next April, so I'm very interested in the 2018 Leaf. When you L2 charge, do you limit the max SOC to 90%? Thanks!

    1. Both are "coined" terms. Gary Giddings an early LEAF pioneer created a kit that decoded CANBUS info and one of the parameters he found was a numerical value for the battery capacity that did not correspond to any known scale and had a value of 80 watt hours (later changed by many to 77.5 watt hours) so for lack of a better name, someone came up with the term GID to honor Gary's work. This was the predecessor to LEAF Spy.

      Hx is a term that came from LEAF Spy development and is another measure of health. Some feel its tracking internal resistance and is closely related to SOH (state of health)

      When I charge its almost always overnight to 100%. My driving needs don't really allow me to "leave some battery at home"

  2. Purchased my 2014 Leaf SV CPO (no QC) in April with 8,700 miles for for $9.8k. I've kept details stats on the battery (see link below). At purchase LeafSpy showed 100% SOH and Hx of 104.28%. In the next 3 months my numbers dropped to the low 90's SOH and Hx.

    M-F I drive very little, working 4 miles from work. But I do try and drive the Leaf as much as possible, mostly like a grandpa, until I ran into a guy on Facebook who has a 13 Leaf with around 43K and all 12 bars.

    Basically he said driving slowly was killing my battery. Having nothing to lose I began experimenting. When the battery gets in the low 90's it will let me juice the pack with pulse driving. B & ECO mode. Pulse up to 4-5 bubbles and let the car coast region for a few seconds. Keep doing this from a full charge (will not work until the pack has room to regenerate) to 32% SOC.

    Last night I was able to make a "pulse" run and take my pack back to 99% SOH until I hit 32%. That number will drop back all week until I can make another run to boost it. What do I have to lose? Maybe my Leaf would have settled at 92% SOH and Hx, but who knows? At the price I paid for the car in 4-5 years I could buy a new pack and still be about $15K in total cost. That's still little money for a lot of car and driving.

    Here are my stats:

    1. Driving slowly does not kill your battery. In fact, it likely will allow your pack to last longer. What you are more likely seeing is a recalibration of the BMS (battery management system) It would appear that for some unknown reason, the BMS loses count and the true capacity but recalibrates its numbers (or relearns the pack) when you get into several cycles where you charge to full and discharge to relatively low SOC (under 30% or thereabouts)

      Your power/regen cycling is causing way more power to flow in and out of your pack and I don't think that is a good idea. What you are doing is increasing your cycle count with minimal benefits.

      The only real thing you can do is simply track your numbers and keep tabs on trends. Graph your data and look at graphs covering a month, 3, 6 12 months, etc. This will also give you a truer picture. The reality is we put way too much into random ups and downs and its our nature to figure out why it happened and create a cause/effect solution which is nice, don't get me wrong. Data is great but sometimes there is simply nothing there.

    2. I have a 30kw Leaf showing 86% SOH after buying it used with a Leafspy report showing 93%. We drive it about 10 miles per day, very light usage. Would driving it harder actually be good for the battery or just for our SOH number/BMS estimate?

    3. HappyFunBall; With your low level of driving, I would just do what you are doing but NEVER charge over 70% SOC. With your very modest need, there is no reason to risk accelerating degradation.

      On days when you need to make the longer trip of say at least 50 miles round trip. Then you can charge to full but its important to minimize the time at high SOC as much as possible especially during warm weather.

  3. I want to degrade my battery so that I can get a free replacement from Nissan's warranty. If I run it down to close to 0 regularly and leave it there and then go to 100 and leave it there how long before I can get down to the 8 bars or less that I need for the warranty to kick in?

    1. No real way to answer that. Degradation has many components and the fastest way to degrade pack is Time plus heat plus High SOC. So the more of the 3 you have, the faster the loss.

      Now you have to keep in mind that Nissan will void the warranty if it detects abuse but in most cases, if you live in a hot climate there is little they can do.

      For more;