I run a BlackJack electric vest. It only draws 35 watts, so even the puniest charging system should be able to run it. The Commando MK3 sotck 180 watt runs it easily. I have also operated the vest with a 90 watt generator on a Vincent, had to shut the vest of if riding at night in slow traffic with that one. The 120 watt alternator on the 650 ss also runs the vest along with headlight and Boyer, but there again I would not leave the vest plugged if going traffic light to traffic at night.
On the open road, no trouble at all and does it ever help to combat the cold.
The vest is the best place to start adding electrically heated items as it warms all the major organs and warms the blood supply to the extremities.
A friend tried wired in heated gloves, they were ridiculously cumbersome. He now has battery operated ones and loves them. He gets 6 hours of running per charge, so with a set of extra batteries on board he is setup for a lot of cold weather riding.
I'll enquire as to what brand his gloves are.
Glen