Oxford HotHands Essential Heated Over-Grips From  £66.49

They are very bulky and make steering feel weird,but that means all your fingers are in contact- so no cold finger tips. they get very (too) hot quickly, even through winter gloves, so you'll be turning them on and of at 10 min intervals (as no levels control).
Finally went out to my bike today, and battery was 100% flat- putting the cover on or the wind moving it about must have knocked the switch into the on position as I know I checked it was off when I left the bike last.

Don’t bother too bulky and I have hands as big as a gorilla