I have been reliably informed that LiFePO4 batteries will actually warm themselves in use (The internal resistance generates a little heat). This means, with a well-insulated battery box (and plenty of fresh-air cooling for during the summer), using and charging the batteries will keep them nicely within their operating temperature.
Of course, another idea would be to funnel “exhaust” air from the cabin through the battery box on it’s way out of the vehicle, too. As LiFePO4 are sealed, there’s no need to worry about gassing (As you need to with PbA). And at –40, you can bet the cabin heater will be running!
So then all you have to worry about is when the vehicle is sitting idle and not charging, say at a place of work with no available outlets. Then you really do have a problem, and it might be an idea to fit some kind of “command start” system for remote warming, or a temperature monitoring device, to ensure the cells don’t get too cold. And I believe it would be quite simple to repurpose a system for ICE cars (yes, they have them – keep your car nice and warm while you pop into the shops, it just idles the gas engine while it waits. Talk about inefficient!) to do a similar task for a battery box.
So, it seems, for Canadian conditions, LiFePO4 cells are the best bet. For now, anyway.
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