[Max Weisel] recently created a Peltier-based cooling/heating system that fits into a backpack. The system uses two Peltier units, each running at 91.2 watts, with computer heat sinks mounted on one side of the unit to dissipate the excessive amounts of heat generated. While he was originally trying to build a cooling backpack, the use of the Peltier units meant that the cool side would become warm when the direction of current was switched, meaning that the backpack could become a heating backpack with the flip of a switch. In order to power the two Peltier units, he uses two 12v motorcycle batteries, weighing in at around 5 pounds each. While this backpack might be a little heavy for your back, it looks promising for anyone who needs to keep things cool (or warm) on the go.