I've just bought one of these that run off a power bank same as you would use to charge a mobile phone. Very warm and fits underneath my waterproof jacket just the job for the cold weather
I just wear a jumper under my coat in the winter but I find I have to undo the zips under the arms as I get too hot, the biggest issue I have is my hands freezing and feeling like I’ve got razor blades in them!Tried all sorts of gloves but don’t like the feel on the pole, even thought about making some sort of heated bike grips!