Here's a link to what I've got:
http://store1950.storeserver-2.com/
It has hi,med,low settings and I like it 'cause it's not
hooked up to the bike, and can't kill it. I got it from
a magazine promo deal that came with a spare battery.
Set on med, you get 4-5 hours of heat per batt.

If this rig isn't enough to keep me warm, I'm not riding!
I've been comfortable down to 27 degrees.

Uncle Charlie