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 where I happend to be. 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 is to keep the SOC at 39.5% 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 athttps://docs.google.com/spreadsheets/d/1GW3yY2nQ18X7M_GhTqpYP5BtN4gR25AMBLCy4rDQil8/edit#gid=206197239