Sorry but I cannot agree with that. There isn't a lot of extra power available on these bikes, especially if you add a sidecar (= more lighting load), which is pretty much necessary if you are really using it in winter.As long as the bike is running, it will not drain the motorcycle’s battery.
Speaking as one of the forum's actual winter riders, I'll stick with my snowmobile gear to keep me warm with the handlebar heaters on as needed.