Which doesn't seem to explain why an unused battery sitting in a partially discharged state would age any faster than one that is being cycled.
Hmm, I have not seen any claims that an unused battery deteriorates
faster than one that is used. I merely thought that people generally expect a battery to maintain its health if unused, but unfortunately it still wears out, although I assume much more slowly. If you have a link to information (preferably from Tesla Motors) claiming that leaving the Roadster sitting unused will age its battery faster than normal use, then please let me know.
I know with the LiFePO4 cells the recommendation for storage is discharge to around 50% SOC and cooler temperatures and ignore them.
Basically the same as the Tesla Roadster Storage Mode, which allows the SOC to drop to 50% and then maintains it there.
My guess, since the Roadster uses power even at rest the cells are charging and discharging somewhat even in storage mode. Over time without being taken to a higher state of charge where balancing occurs the cells could get out of balance. A full cycle or two every now and then would allow full balancing as well as show up any weak cells.
Does anyone have numbers on how high the SOC must be for balancing to occur? Also, what damage occurs if cells are unbalanced? As far as I understand, the 69 paralleled cells in a brick would automatically balance, and the 99 series bricks should not really care whether they all have balanced voltages - unless, of course, one brick could drift significantly above or below the ideal 50% SOC for storage (but I assume that 50% target has a high degree of slop ... it doesn't have to be precisely 50%, does it?).
