Lately on the Greenway the still water ponds, lakes, and swamps have been thinly glazed over with ice. So, here's a solution of mine for cold batteries. Riding my ebike to the trail, then it sits in the cold for an hour or more. Similarly, riding to the trail the EGO batteries I use for my Onewheel had been subjected to the cold of the trip.
Solution? I mounted a beer cooler to the rear rack on the ebike, behind the Onewheel. In the cooler in a towel I put a couple of warm red clay bricks straight off my fiery, active wood stove. Then for the trip out, in the cooler I put my EGO batteries. When I park and lock the ebike on the trail, I trade, and put the ebike batteries in the cooler. The heated bricks keep everything warm -- for the trip, and for hours.
