I personally hate being cold. Thin blood perhaps, but being comfy and having hands that can feel the levers is vital for safety, I agree.
I now have visions of me togged head to foot in batteries, I’ll weigh more than the bike 
+1 for Gerbing, in winter I wear heated insoles, jacket and gloves. I think a ride in cold weather of around an hour I’d manageable but if you are out all day in close to minus numbers then heated clothing is for the way to go, comfortable riding even through cold nights.
Don’t worry about the batteries. The draw on the charge system is negligible. It’s only a problem if you have a charge fault, use the gear on higher settings when stopped.
Good luck
Steve
I have often thought about heated grips on my Convert, but with the battery flattening with lights on, on a long pootle with two slow riders, I’d be worried that I’d be stuck again and not able to start or bump start.