AME hand warmers. They are designed to shut down if the battery voltage drops below a certain point. They work great. I had a Trail tech stator in my bike. Like I said earlier switching to the new Lithium battery is the ticket. The batteries are so small you could actually put two in if you wanted to. After I switchd to the new style battery I never used my jumper pack again. Just remember to bump start 3 or 4 times before cranking on it to warm up the battery.