Living the Leaf Life Below 40% SOC and pulse driving - battery protection strategy

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jim0266

Well-known member
Joined
Mar 17, 2017
Messages
82
Location
Akron, Oh
By accident I may have discovered a weird Leaf battery quirk that could benefit a small group of Leaf drivers who drive short distances. This turned into a long post but I hope someone finds it useful.

Some background first. I’m about 15 months into ownership of my 2014 Leaf SV, purchased as a CPO with only 8,750 on the odometer for $9,800. The car was still showing 100% SOH at purchase with 67.36 AHr and 104.28% Hx as reported by LeafSpy.

Viewing this purchase as an experiment, I started keeping detailed records of my battery health and amount of charging.

My work commute is a massive 9 miles RT, where I also have free L2 charging in our parking deck. This short trip and small trips of about the same range around town constitute the majority of my Leaf trips. Other journeys are less frequent, but are to nearby towns that average around 90 miles for the RT. I charge at the destination before returning home.

About two months after purchase my battery health plunged to 91% SOH, 60.01 AHr and 91.83% Hx. I assumed the age of the car was the main culprit for the battery stats. After all, I was babying the car and grandpa driving. I was only at 10,300 miles.

That’s when I bumped into someone who clued me in to pulse driving. My Leaf Yoda explained all the grandpa driving was killing my battery. He recommended L3 charging the car and pulse driving. My Leaf cannot QC, which seems helpful to others with good battery stats over time. The theory is pulse driving mirrors the effects of quick charging.

I started finding excuses to take the car on longer trips and pulse drive. My battery SOH soon climbed back to 100%. Keeping my SOC in the mid-to-high 90’s did take effort. As soon as I reclaimed the numbers they would immediately start falling the next day. Once a week I needed to work the battery to keep the numbers high.

My current technique for pulse driving is while in ECO > D mode I keep repeating gentle accelerations to 4-5 power bubbles and lift off the accelerator for a few seconds and keep repeating this process. I start with 100% SOC. The technique starts working around 95% SOC when you regain the double regen bubbles. It works down to 32% on the dash, which is 40% SOC in LeafSpy. Secondary roads with sparse traffic where I can keep speeds around 55mph are perfect for this.

I started in Eco > B mode for pulse driving and generated as many power bubbles as possible. I have found no advantages in this mode or going above 4-5 power bubbles. It heats the battery faster and makes my wife nauseated due to the stronger regen. In ECO mode it's also easier to keep to 4-5 power bubbles due to the less responsive accelerator pedal.

Pulse driving was also finicky as to when the battery was ready to accept these shocks and bring up the stats. Some sessions saw my battery pack hungry to add Hx while other times it rose grudgingly. When pulse driving you can watch the Hx numbers rise in real time in LeafSpy. The AHr number resets pretty quickly but the SOH numbers take longer to reset, usually at least a few hours.

Once winter arrived and the battery temp of the pack dropped into the 40’s, my battery stats also froze at 100% SOH (no matter what level SOC on the battery). I didn’t pulse drive all winter. I was now closing in on 19k miles.

Winter seemed to show the benefits of a thermally managed pack.

The arrival of spring brought battery pack temps back into the 50’s and the battery stats once again started to plunge. Now, however, I could not keep the SOH above 94%.

Whenever I ended a pulse driving session I would leave the car at a low SOC overnight, above 30% SOC but below 40% (as reported by LeafSpy) to minimize degradation overnight while the pack cooled off. The pack temp would often end in the high 80’s sometime in the low 90’s after pulse driving. That golden zone, according to a chart I found online, claims to show the zone for the least amount of battery degradation according to SOC and and battery temp. At 90F battery temp that is between 30 and 40% SOC.

Since I have a short commute and working L2 charging (as well as L2 at home), once summer arrived I kept my SOC in the golden zone for the leaset amount of battery degradation when ambient temps alone drove the battery pack temp into the 80’s.

That’s when I noticed something odd. I was stopping my charging sessions no higher than 39.6 SOC because 40% (as reported by LeafSpy) is when pulse driving stops working. My battery stats also froze. For two weeks not going above 40% SOC my SOH has remained locked at 93.53%, 91.93% Hx and 61.17 AHr. Thanks to my short daily commute and L2 charging at home and work, it's easy to live in this narrow band of charge. 40% SOC is the tipping point. I charged to 40% at work one day and went down a steep hill a half mile away and regened over 40% and the stats dropped a tiny amount.

After several weeks of normal charging above 40% and making short trips around town, from past experience my battery stats would have plunged. My SOH had gone as low as 88.63% this spring.

The real test of living below 40% SOC came on my golf league night. The course is 11 miles away. I left work with 39.5% SOC and arrived with 33.2% SOC charge remaining. I eco-drove the hell out of that run, which is all back roads. Home was the same distance away so I had plenty of charge remaining. It's amazing how far you can go when eco driving.

The next test was to charge to 100% and take a long drive using the pulse driving technique once our summer temp dropped to something reasonable and my pack temp was at least in the 70's. The destination was about 40 miles away and offers two good, free L2 charging stations a few miles apart. Both use renewable resources for their power as well, a nice bonus.

I feared my stats would plummet and the battery would be stubborn after several weeks of living below 40% SOC. My Hx initially dropped from 91.93% to 91.84% (LeafSpy will show you these changes in real time) for the first 20 miles or so before slowly starting to climb. Near the end of our destination the Hx value started to rise faster. We arrived at our destination with the Hx value now at 93.16%, up from 91.93% at the start.

We returned from dinner to just shy of 80% SOC. Close to home we hit 40% in LeafSpy (32% on the dash), where pulse driving stops working. The Hx value had risen to 95.59%. I left the car around 35% SOC overnight with the battery pack at 93.8F. That's still 6 temperature bars.

Next morning the AHr value had reset to 63.79 and the SOH to 97.54%. Over the next two days I drove around town staying below 39.5% SOC and my battery stats have stayed the same.

Going forward my plan when the ambient temps raise the battery temperature into the low 50'sF is to keep the SOC at 40% at the highest and charge to 100% and pulse drive when taking longer trips.

There are currently 20,800 miles on my Leaf.

View my battery stats at
https://docs.google.com/spreadsheet...qpYP5BtN4gR25AMBLCy4rDQil8/edit#gid=206197239
 
jim0266 said:
About two months after purchase my battery health plunged to 91% SOH, 60.01 AHr and 91.83% Hx. I assumed the age of the car was the main culprit for the battery stats.

No, your original statistics were probably due to a BMS reset or similar "pulse driving".

Leafspy just reports on what the BMS estimates the battery capacity is. The BMS can be fooled. Fooling the BMS doesn't improve the battery. Resetting the BMS doesn't improve capacity. Recharge and range tests confirm this.

DCQC and high discharge and regeneration probably wear the battery faster.
 
Wow,, that's a long post. Hard to follow along..

So, let me see if I get this correct:

1. If I drive short trips (eg, less than 10 miles a day), I should pulse drive (which means to repeatedly accel and let off of the pedal, instead of holding the pedal steady?)...

2. And to keep the the SOC (as shown in the cluster display) to around 40% (which is about 4-5 bars)? And charge up to what SOC? 80%?
 
Ok, I think that I will try something like this for a few weeks. I've got nothing to lose because my commute is 8 mi RT and I'm down to 9 bars on my 2011. If I can regain something I'll let you know. FYI, I've kept my average SOC fairly low for the the past 7 years, but still have seen significant calendar degradation with less than 50,000 mi so far.
 
be236 said:
Wow,, that's a long post. Hard to follow along..

So, let me see if I get this correct:

1. If I drive short trips (eg, less than 10 miles a day), I should pulse drive (which means to repeatedly accel and let off of the pedal, instead of holding the pedal steady?)...

Sorry, this is not what I was saying.

Like you on many days I only drive 9 miles RT to and from work. I leave in the morning with 36-39% SOC as shown in LeafSpy. I arrive at work with 33-34% SOC. I top off to 39.5% SOC at work and drive home. I do not pulse drive around town at a low SOC. My goal is to keep the battery pack at a low SOC for the battery temp. My battery pack temp was 78.3°F tonight when I got home from work. All did was drive it gently to and from work today. A battery SOC of 38% is smack in the middle of the golden zone for the least amount of battery degradation so that's were it sits tonight.

be236 said:
2. And to keep the the SOC (as shown in the cluster display) to around 40% (which is about 4-5 bars)? And charge up to what SOC? 80%?

4-5 bars is too many. You need LeafSpy to see the exact SOC.

When I'm only running around town I have not been charging past 39.5% SOC. I could probably drive 30-35 miles on 39.5% SOC if needed in good weather. If I come home with 20% SOC I charge back to 39.5%.

My new strategy if I make longer trips, say 40 to 60 miles (80-120 miles RT), is to charge to 100% right before departure and pulse drive on that trip. I recharge at my destination and pulse drive back. Then the car will stay around 35-38% SOC once I'm back home.
 
jim0266 said:
be236 said:
Wow,, that's a long post. Hard to follow along..

So, let me see if I get this correct:

1. If I drive short trips (eg, less than 10 miles a day), I should pulse drive (which means to repeatedly accel and let off of the pedal, instead of holding the pedal steady?)...

Sorry, this is not what I was saying.

Like you on many days I only drive 9 miles RT to and from work. I leave in the morning with 36-39% SOC as shown in LeafSpy. I arrive at work with 33-34% SOC. I top off to 39.5% SOC at work and drive home. I do not pulse drive around town at a low SOC. My goal is to keep the battery pack at a low SOC for the battery temp. My battery pack temp was 78.3°F tonight when I got home from work. All did was drive it gently to and from work today. A battery SOC of 38% is smack in the middle of the golden zone for the least amount of battery degradation so that's were it sits tonight.

be236 said:
2. And to keep the the SOC (as shown in the cluster display) to around 40% (which is about 4-5 bars)? And charge up to what SOC? 80%?

4-5 bars is too many. You need LeafSpy to see the exact SOC.

When I'm only running around town I have not been charging past 39.5% SOC. I could probably drive 30-35 miles on 39.5% SOC if needed in good weather. If I come home with 20% SOC I charge back to 39.5%.

My new strategy if I make longer trips, say 40 to 60 miles (80-120 miles RT), is to charge to 100% right before departure and pulse drive on that trip. I recharge at my destination and pulse drive back. Then the car will stay around 35-38% SOC once I'm back home.

Ok, this is opposite to what I read earlier.. that it's better to do ONE long charge, say from 20% to 80%, instead of multiple short charges of 20% to 30% (this seems so inconvenient?)... Yeah, I really need to get LEAF Spy.. but I ordered an ODB2 unit, it was supposed to be v1.5, but turned out to be v2.1, which dont work with LEAF Spy.
 
jim0266 said:
By accident...
The AHr and SOC numbers take longer to reset. The SOC numbers reset in a few hours while the AHr number usually takes until the next day to reset.
...
I assume when you write "SOC" here you mean "SOH". The other occurances of SOC and SOH look correct.

How can you distinguish whether your acceleration-and-regeneration actually gives you more battery capacity, as opposed to giving you better BMS/LeafSpy numbers for the same underlying battery capacity?

I haven't read anyone here on MNL speculating on how the BMS comes up with its AHr and SOH numbers. I would guess it's a function of measured voltage times measured amperage, integrated over time, then extrapolated to the 0..100% range.
 
Thanks, I did mean SOH.

I'm not sure how I would test that practically. I'm stuck believing the numbers LeafSpy gives me. Below are three sets of numbers from Leafspy when I charged to 100%. The oldest is when the numbers bottomed out a few months after purchase. The second sent is after two months of pulse driving. The 3rd set is the last time I have numbers from a 100% charge last month.

As of 7/23/18 my SOH is back to 97.54%

If I had kept driving the same way I was back in March of 2017 I cannot believe I would have the numbers I have today.

4/16/17
SOC 96.9%
SOH 91%
Gids 260
Ahr 60.11
395.95V
Miles 9,305

6/18/17
SOC 97.0%
SOH 100%
Gids 284
Ahr 66.65
395.45V
Miles 11,065

6/13/18
SOC 97.1%
SOH 92.09%
Gids 261
Ahr 60.23
395.96V
Miles 20,100
 
WetEV said:
jim0266 said:
About two months after purchase my battery health plunged to 91% SOH, 60.01 AHr and 91.83% Hx. I assumed the age of the car was the main culprit for the battery stats.

No, your original statistics were probably due to a BMS reset or similar "pulse driving".

Leafspy just reports on what the BMS estimates the battery capacity is. The BMS can be fooled. Fooling the BMS doesn't improve the battery. Resetting the BMS doesn't improve capacity. Recharge and range tests confirm this.

DCQC and high discharge and regeneration probably wear the battery faster.

@WetEV, how can you tell the difference between fooling the BMS and doing things that are actually good for your battery? I've read that the LeafSpy battery stats are kind of meaningless over the short term, like a few months, but I'd think that over 15 months, they would at least mean something.

In the 2+ months I've had my car, I have noticed that babying the battery makes the LeafSpy stats go down, and getting the car to really stretch its legs -- longer distances, freeway driving, deeper discharges and recharges -- makes them go up a bit. I get that those numbers may not be accurate, but in that case, how can I measure and determine what's good for my car?

I've been tracking battery percent discharged as a function of miles driven, but that ratio is all over the place due to varied driving conditions.

Thanks.
 
Silverfish said:
how can I measure and determine what's good for my car?.

If I wanted to measure actual capacity, I'd discharge/recharge a few times with L2, then park in a climate-controlled garage at 70F, L2 charge to 100%, then put the car ON, and attach a 1kw resistive load to the 12v system. and count the hours abd minutes until turtle. Could be 24 hours or so. This could be repeated , as a better "annual battery check".
 
Silverfish said:
WetEV said:
Leafspy just reports on what the BMS estimates the battery capacity is. The BMS can be fooled. Fooling the BMS doesn't improve the battery. Resetting the BMS doesn't improve capacity. Recharge and range tests confirm this.

DCQC and high discharge and regeneration probably wear the battery faster.

@WetEV, how can you tell the difference between fooling the BMS and doing things that are actually good for your battery? I've read that the LeafSpy battery stats are kind of meaningless over the short term, like a few months, but I'd think that over 15 months, they would at least mean something.

In the 2+ months I've had my car, I have noticed that babying the battery makes the LeafSpy stats go down, and getting the car to really stretch its legs -- longer distances, freeway driving, deeper discharges and recharges -- makes them go up a bit. I get that those numbers may not be accurate, but in that case, how can I measure and determine what's good for my car?

What follows is my mostly opinion.

I think that the battery true capacity is mostly declining with time. Faster for deep discharge/charge cycles, faster for high rates of charge/discharge, faster at high levels of charge or low levels of charge and faster at higher temperatures. Slightly faster for the first 5% of decline, then slower, then faster somewhere below 70% capacity.

I think that most variation of the BMS statistics that LeafSpy reports is just inaccuracies in the estimate, and not real changes. I don't have measurements accurate enough to prove this. In a few months last fall, I measured my LEAF's battery capacity with a L2 recharge test at temperature of 20C, then tried to increase the BMS estimate by DCQC, faster driving, deeper discharge and a few other tricks, then to tried to reduce the BMS estimate by slow L2 charge (8 Amp L2), local driving only, keeping charge near 50%, shallow charge cycles. The result was that the BMS estimate can be 12% or more larger capacity than real, and perhaps 2% to 3% percent less than real. This is making the assumption that the real capacity doesn't change much over a few months, and variations in driving/charging don't actually change real capacity.

So how could I take measurements with the BMS that vary +12% to -3% from real capacity and find the trend of declining capacity which is about 2.5% to 3% a year in my case? With at least a few months every year of consistent driving in consistent temperatures and such and a few years of records, I think this is a realistic goal, however isn't easy as your life changes, and as year to year weather may be different. This gets harder on a shorter term basis, but on a year to year period might be fairly accurate.

So how could find the smaller variations in that small trend caused by different charging rates, driving styles, depth of charge/discharge cycles and so on? What makes this problem even worse is that the BMS software has been updated at least on some cars, the battery chemistry has changed over the years and so forth... I don't think there is an easy way to use BMS statistics to really tell what's good for the car. It seems to me that it would take years and multiple cars to get to a believable answer. It would be easier to use a more accurate way of measuring battery capacity, and multiple cars driven in the same conditions with different charge rates, depth of charge/discharge cycles, etc. But with one car? You are looking at a tiny needle in a large haystack. The haystack is fuzzed up because of BMS inaccuracy. I don't think you can tell the difference between "fooling the BMS and doing things that are actually good for your battery", at least with one car and a reasonable amount of time.
 
WetEV said:
Silverfish said:
WetEV said:
Leafspy just reports on what the BMS estimates the battery capacity is. The BMS can be fooled. Fooling the BMS doesn't improve the battery. Resetting the BMS doesn't improve capacity. Recharge and range tests confirm this.

DCQC and high discharge and regeneration probably wear the battery faster.

@WetEV, how can you tell the difference between fooling the BMS and doing things that are actually good for your battery? I've read that the LeafSpy battery stats are kind of meaningless over the short term, like a few months, but I'd think that over 15 months, they would at least mean something.

In the 2+ months I've had my car, I have noticed that babying the battery makes the LeafSpy stats go down, and getting the car to really stretch its legs -- longer distances, freeway driving, deeper discharges and recharges -- makes them go up a bit. I get that those numbers may not be accurate, but in that case, how can I measure and determine what's good for my car?

What follows is my mostly opinion.

I think that the battery true capacity is mostly declining with time. Faster for deep discharge/charge cycles, faster for high rates of charge/discharge, faster at high levels of charge or low levels of charge and faster at higher temperatures. Slightly faster for the first 5% of decline, then slower, then faster somewhere below 70% capacity.

I think that most variation of the BMS statistics that LeafSpy reports is just inaccuracies in the estimate, and not real changes. I don't have measurements accurate enough to prove this. In a few months last fall, I measured my LEAF's battery capacity with a L2 recharge test at temperature of 20C, then tried to increase the BMS estimate by DCQC, faster driving, deeper discharge and a few other tricks, then to tried to reduce the BMS estimate by slow L2 charge (8 Amp L2), local driving only, keeping charge near 50%, shallow charge cycles. The result was that the BMS estimate can be 12% or more larger capacity than real, and perhaps 2% to 3% percent less than real. This is making the assumption that the real capacity doesn't change much over a few months, and variations in driving/charging don't actually change real capacity.

So how could I take measurements with the BMS that vary +12% to -3% from real capacity and find the trend of declining capacity which is about 2.5% to 3% a year in my case? With at least a few months every year of consistent driving in consistent temperatures and such and a few years of records, I think this is a realistic goal, however isn't easy as your life changes, and as year to year weather may be different. This gets harder on a shorter term basis, but on a year to year period might be fairly accurate.

So how could find the smaller variations in that small trend caused by different charging rates, driving styles, depth of charge/discharge cycles and so on? What makes this problem even worse is that the BMS software has been updated at least on some cars, the battery chemistry has changed over the years and so forth... I don't think there is an easy way to use BMS statistics to really tell what's good for the car. It seems to me that it would take years and multiple cars to get to a believable answer. It would be easier to use a more accurate way of measuring battery capacity, and multiple cars driven in the same conditions with different charge rates, depth of charge/discharge cycles, etc. But with one car? You are looking at a tiny needle in a large haystack. The haystack is fuzzed up because of BMS inaccuracy. I don't think you can tell the difference between "fooling the BMS and doing things that are actually good for your battery", at least with one car and a reasonable amount of time.

Thanks.

At this point, I'm mostly tracking the car's reported battery percentage and the trip meter, to get a sense of how many miles per battery percent the car can go. There's a lot of variation depending on driving conditions, but the averages don't seem to have decreased over the last couple of months, even though the LeafSpy stats have.

I have to admit, though, that it is unsettling to see those LeafSpy numbers go steadily down. I guess I'll have to just trust that babying the battery is my best option and start ignoring LeafSpy.
 
Ran across this article of a gentleman in NZ doing the same thing with his 2012 Leaf by keeping the SOC below 40% as he also drives short distances.

Early adopters as teachers: a case of extraordinary care of a Leaf battery
https://flipthefleet.org/2018/early...case-of-extraordinary-care-of-a-leaf-battery/

"The goal was to minimise battery degradation using optimum charging practices, identified as shallow depth-of-discharge, frequent part-charging, and as far as possible to keep charge level at or below a level considered best practice for storage (30-40%). Web discussion papers suggest that li-ion batteries are most stable at 3.92 cell voltage; a SoC level of 39.0% gives a maximum cell voltage of 3.925v for the Leaf under discussion."
 
jim0266 said:
Ran across this article of a gentleman in NZ doing the same thing with his 2012 Leaf by keeping the SOC below 40% as he also drives short distances.

Early adopters as teachers: a case of extraordinary care of a Leaf battery
https://flipthefleet.org/2018/early...case-of-extraordinary-care-of-a-leaf-battery/

"The goal was to minimise battery degradation using optimum charging practices, identified as shallow depth-of-discharge, frequent part-charging, and as far as possible to keep charge level at or below a level considered best practice for storage (30-40%). Web discussion papers suggest that li-ion batteries are most stable at 3.92 cell voltage; a SoC level of 39.0% gives a maximum cell voltage of 3.925v for the Leaf under discussion."

Interesting. Good to have another data point.
 
jim0266 said:
Ran across this article of a gentleman in NZ doing the same thing with his 2012 Leaf by keeping the SOC below 40% as he also drives short distances.

Early adopters as teachers: a case of extraordinary care of a Leaf battery
https://flipthefleet.org/2018/early...case-of-extraordinary-care-of-a-leaf-battery/

"The goal was to minimise battery degradation using optimum charging practices, identified as shallow depth-of-discharge, frequent part-charging, and as far as possible to keep charge level at or below a level considered best practice for storage (30-40%). Web discussion papers suggest that li-ion batteries are most stable at 3.92 cell voltage; a SoC level of 39.0% gives a maximum cell voltage of 3.925v for the Leaf under discussion."

Hi Jim - thanks for the FtF contact re above. Thought any discussion may possibly benefit others here.

My thinking now is that the BMS is designed not to function below 40% SoC, a Nissan mechanism to allow batteries stockpiled for the production line, and transported subsequently, to remain at 100% until sale time perhaps many months ahead. My Leaf was stockpiled for 26 months before I bought it as a new car, with SOH at 96%. No doubt calendar ageing is still occurring, but the stable numbers have a "feel good" factor. The main benefit is the stability offered by the 3.9v cell level.

On your longer trips I think the 100% charge is the key to your better metrics; the battery becomes optimally balanced for a while, returning the best range and boosting range related data. A spell under 40% tends to do the opposite, with an increasing cell voltage delta (not that it matters for short trips).

So, for long battery life: choose a temperate climate to live in (my annual battery temperature range is about 13-25C), keep the battery below 40% as much as possible (2 charge bars or less), charge only as much as required, and only when needed (the car timers can make this easy), and build in one regular 100% charge/fairly full discharge cycle every month or two, to maintain reasonable pack balance.

Just my 2c worth :)
 
Thanks hieronymous for weighing in. I do agree about the feel good factor. It's a grand experiment.

I also sent you a PM.
 
Update:

Finally made a long 108 mile RT pulse-driving run (lunch with mom :D ). I L2 charged to 100% (97.1% actual) at home. LeafSpy reported 275 GIDS on a full charge. This was the first time in 34 days I’ve charged beyond 40%. I drove 406 miles in between these dates.

Starting stats:
Hx 95.18%, SOH 97.05%, Ahr 63.47

The battery lost Hx values all the way to my destination. I arrived at my destination around 44% SOC and L2 charged back to 89%. Around 77% SOC on the way home pulse driving started to increase the Hx values. Hx dropped as low as 92.58% before rising.

Ending stats:
Hx 93.90%, SOH 95.53%, Ahr 62.48

Over the last month if I had gone above 40% SOC I would have had to work to keep these numbers.

As I make longer runs over time it will be interesting to see if the pack is more or less responsive to my pulse driving. Even when I was pulse driving on a regular basis I could never predict if the pack would be willing to accept the shocks or be recalcitrant like on this run. The first long trip I made after keeping <40% for 3 weeks the pack went from 93% to 97% SOH, where it stayed until I made this trip.

My 14 Leaf now has 21,420 miles.

I've also started to track my GIDS to look for changes over time. Recent readings end of July to date:

SOC GIDS

39 86
39.1 84
39.1 85
39.1 88
39.2 86
39.2 82
39.6 86
39.7 87
39.8 87
39.8 86
39.8 87
39.8 87
39.8 88
39.8 86
39.9 90
39.9 90
39.9 84
39.9 88
40 88
40 90
 
Update after another 1,000 miles of living below 40% during a hot summer.

Stats from last post, 62.48 AHr, 95.53% SOH, 93.90% Hx, stayed stable over the past 6 weeks. I made two longer-range pulse drives this weekend. The first drive went from 100% SOC to low 30's. Numbers dropped to:

60.82AHr - 93.00% SOH -- 91.93%Hx

The following day charged back to 100% and made 40-mile pulse drive where Hx dropped to 91.51%. Charged at destination back to 91% and pulse-drove down to 40% on Leafspy and finished drive around 32%. This time the battery pack was receptive to the pulse hits. Finished the drive at:

62.95 AHr- 96.26% SOH - 94.51%Hx

I'm now slightly up from my last period of staying below 40% SOC.

Charging back to 40% I reached 94 GIDS. Prior period I usually reached 84 GIDS. My 2014 Leaf now has 22,212 miles.
 
hieronymous said:
jim0266 said:
Ran across this article of a gentleman in NZ doing the same thing with his 2012 Leaf by keeping the SOC below 40% as he also drives short distances.

Early adopters as teachers: a case of extraordinary care of a Leaf battery
https://flipthefleet.org/2018/early...case-of-extraordinary-care-of-a-leaf-battery/

"The goal was to minimise battery degradation using optimum charging practices, identified as shallow depth-of-discharge, frequent part-charging, and as far as possible to keep charge level at or below a level considered best practice for storage (30-40%). Web discussion papers suggest that li-ion batteries are most stable at 3.92 cell voltage; a SoC level of 39.0% gives a maximum cell voltage of 3.925v for the Leaf under discussion."

Hi Jim - thanks for the FtF contact re above. Thought any discussion may possibly benefit others here.

My thinking now is that the BMS is designed not to function below 40% SoC, a Nissan mechanism to allow batteries stockpiled for the production line, and transported subsequently, to remain at 100% until sale time perhaps many months ahead. My Leaf was stockpiled for 26 months before I bought it as a new car, with SOH at 96%. No doubt calendar ageing is still occurring, but the stable numbers have a "feel good" factor. The main benefit is the stability offered by the 3.9v cell level.

On your longer trips I think the 100% charge is the key to your better metrics; the battery becomes optimally balanced for a while, returning the best range and boosting range related data. A spell under 40% tends to do the opposite, with an increasing cell voltage delta (not that it matters for short trips).

So, for long battery life: choose a temperate climate to live in (my annual battery temperature range is about 13-25C), keep the battery below 40% as much as possible (2 charge bars or less), charge only as much as required, and only when needed (the car timers can make this easy), and build in one regular 100% charge/fairly full discharge cycle every month or two, to maintain reasonable pack balance.

Just my 2c worth :)
Hieronymous, I've followed your elegant data-rich posts with interest, and thank you for them. Right now, I'm a little confused on two counts. First, you seem to be postulating that if SOC is kept chronically below 40% the BMS algorithm considers the vehicle unsold and doesn't register any loss of capacity. But if that's the case, doesn't that complicate the interpretation of a lot of your carefully collected data, and if so, what is your rationale for maintaining your conclusion that 30-40% is the optimal resting charge level?

Second, you say that the optimal maximum cell voltage for preserving the capacity of lithium iron batteries is 3.92 V, and I've seen that stated elsewhere. But according to Leaf Spy measurements of my 2019 40 kWh Leaf, to achieve that the SOC needs to be 70-75%. As I write this, the vehicle is at 60% SOC (according to Leaf Spy, 55% according to the dash), has been sitting undriven in the garage for over 20 hours, and (with charger unplgged and climate control off) the maximum cell voltage is 3.77 volts.

I'm really enjoying my new Leaf and want to keep it as long as possible. I've been following your advice for the most part, but it would certainly be more convenient to charge to 75% instead of 40%!

I invite hieronymous and other forum members to weigh in on this, as I know your advice will be worth a lot more than $0.02!
 
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