Noal wrote:mux wrote:It really depends on where you draw the line. Want to keep the battery in tip-top shape? Blanket, PTC heater, pretty high temperatures. Want to just barely scrape by? Probably keep it insulated or in a garage at more than the rated minimum temperature (which is -25C in this case).
My understanding was that 18650 are rated for discharge at -25C.
But how can we change our batteries at -25C? Or -17C?
Or we must keep range extender battery always above 0C (in case car starts charging)
This is really dependent on the chemistry, and the only way to know for sure is to consult the datasheets or ask an applications engineer. Samsung SDI and Panasonic have very friendly FAEs if you e-mail their battery divisions.
As a general rule, you don' t want to charge the battery under 0C. It will charge, but it will be relatively inefficient and certainly much slower than at above-freezing. For most car-sized batteries, it is actually more efficient to simply pre-heat the battery to about 10C and charge from there; there is not that much thermal mass in the cells and the efficiency easily compensates the losses in heating.