dhanson865 said:
If it is programmed not to come on and waste power when the temp is below the threshold for heat degradation it won't decrease battery life at all in cool areas.
A TMS might also
increase battery capacity in very cold weather by heating it, in particular if it could be done while still plugged-in. It would also help cold weather regen, something that is important where I live.
I realize that the PNW folks have been reveling in their greatly reduced battery degradation compared to the majority of the country, which is warmer. But it isn't just climate: I live in a cool climate — cooler than many parts of the PNW — but I had significant battery degradation. Why? Because I drive steep hills
all the time and the high power levels required to do that caused substantial battery heating! After two years my range was so reduced that if it were not for a newly opened public L2 charge station I wouldn't have been able to make my routine 70 mile grocery shopping trips.
Perhaps someday battery chemistry will be sufficiently heat resistant to have minimal degradation without TMS.
But we aren't there yet. One advantage of the coming larger batteries in the LEAF 2, and other EVs, is that the extra energy cost of running the TMS becomes almost irrelevant because range is not limiting. I charge my Model S60 to 50% or 60% and can easily make my routine local trips. I only charge to 90% when I want to make a long trip (something I did a lot when I first got the car and did 8000 miles in just over three months, including a trip to Portland and Seattle).
You can make the valid argument that the TMS wastes energy but I drive on solar power and pay
nothing for electricity so I really don't care. I even run the AC at times when it is hot, something that I almost never did in the LEAF. I still drive fairly efficiently (once a hypermiler, always a hypermiler?) although usually not below the speed limit as with the LEAF. But I think that those who are driving range-limited cars now might be very surprised how liberating it is to have a car that has more than enough range to handle all local driving without thinking about it. The idea that TMS will decrease range slightly becomes completely irrelevant.
My 2¢.