Stanton said:
SanCarlosJeff said:
The last time I drove my Leaf was March 14. I charged it to 100% that day and then unplugged it. This thread got me to thinking that I should go take a look at the charge level. I was very surprised/impressed to see that the battery charge is now at 99%.
That's the point: the longer your battery sits near 100%,
the the more its long-term health deteriorates.
Lithium batteries are designed to "hold their charge" (that's why they work so well in our cars), but don't like to be stored at/near 100% (especially in warm environments).
TLDR: Correct.
This source is behind a paywall. Sorry.
Also is for a different chemistry, one that might had a use for a product I might have designed. Things are strange now. Remember that different chemistries have different properties, but generally similar behavior. These results are not directly usable for a LEAF, or for any other EV. This is not an automotive battery being tested.
http://dx.doi.org/10.1016/j.jpowsour.2013.09.143
The Leaf doesn't allow for an actual 100% charge, but only about 95%. The LEAF SOC gauge reports 100% at about 95% actual capacity, to say this another way.
For the cell tested in the above source, life at storage at 50C at 100% SOC was 107
days to 80% of initial capacity.
Life at 95% true SOC (or LEAF reported 100%) was a bit less than a year. Storage lifetime increased with decreasing SOC, exceeding 4 years at 50C at low SOC. Much longer calendar life at lower temperatures for all SOCs, see Arrhenius. However directly testing them becomes a challenge.
Now how does that apply to the LEAF? This isn't an automotive battery, but the same general principal does apply. Longer life at lower SOC.
Very bad things also happen at low SOC, below about 30%, but not due to calendar losses, but rather due to cycling losses and probable Li plating.
So store the traction battery at about 40% SOC, unless you might need to do a significant drive without charging. Avoid storage above about 70%, if you can help it. Avoid discharge below 30% SOC, if you can help it. 20% SOC isn't so bad, but 10% SOC and 5% are worse.