Hi Tom
tomsax said:
Hi Dave,
Interesting post. Thanks for the great write-up.
You are clearly technical and dedicated to careful measurements and managing your battery pack. It's a pretty small investment to get LeafSpy going. I'm an iPhone user, but bought a cheap Android just so I could use LeafSpy. Now there's an iPhone version. It requires a specific BlueTooth LE dongle which is more expensive than the ones the Android can use, but either way the cost of hardware and software is still a bargain for what you get.
Yeah, I was surprised and pretty disappointed at losing a bar at 15000 miles while thinking I was being nice to the battery and when others are going twice or triple that....Drat. I hope the previous owner was mean to it and brought it to the edge of the 15% capacity loss just before I got it and I just nudged it over.
I know that LeafSpy is a useful tool in monitoring SOH of the Leaf. But I've been through so many obsolescence cycles of consumer electronics and software... It's not the money, I'm just not keen on dedicating the time to getting an Android device, learning enough about installing and using software on it for just scanning the Leaf battery. Generally I find the "you just type 'setup' and you're done" claim to be false frequently enough to make a smooth install & use less than a 50/50 proposition. Been there with more than one OBD laptop scanner package, Palm, Blackberry, going all the way back to a Radio Shack Model I pocket computer.
And I don't want to get too obsessive/compulsive on the battery. Knowing that cell pair #17 is a little undercharged compared to #18 and #16 isn't going to change how I treat the car and I don't have any control over the battery management system.
If there is a LeafSpy rental service, I'd be interested.
It would be helpful to add your experience to the Plug In America Leaf Owner Survey.
http://www.pluginamerica.org/surveys/batteries/leaf/
I'll do that. Modern BEVs have so little history compared to more than a century of ICE refinement that it's a good time to be an observer/participant. Things are changing fast.
Early results from the survey show no measurable impact between charging to 80% vs. charging to 100% (see the survey paper). Not many people manage their SOC as carefully as you are, so it would be great to add a record of your experience over time to the survey.
My strategy came from reading about failure modes of lithium battery technology. In a nutshell, it appears that you kill capacity with a high state of charge and elevated temperature. These conditions break down electrolyte and form a solid electrolyte interface that essentially plugs up the anode. I understand that there are other mechanisms including thermal & physical damage stemming from high current draw (maintaining constant power output) at low cell voltages (low SOC) and I'm trying to not go there by staying in the 30-60% SOC. I think the battery management system also protects the last 15% or so. It just doesn't let you use that part of the battery.
One thing I haven't found in my reading is anybody trying to remove the SEI once it forms. Lots of additive brews to try to keep it from forming but nobody trying to wash it off or dissolve it once it forms. Maybe I just wasn't reading in the right papers.
Nissan may have goofed by gambling that they didn't need active (expensive) pack temperature management. That's just one of a bazillion engineering decisions and it only came to the surface because they might have been just a little wrong. I have lots of sympathy for that team. It's a lot easier to be wrong than right.
I hope I can compensate some by keeping my SOC in the middle. Too high kills capacity, too low makes the car useless. We'll see how long it takes to lose the next (6.25%) bar. That'll at least give me 2 data points on my capacity loss curve.