Hotronic Battery Pack E3 Bootwarmers 2014 - The Hotronic Battery Pack E3 is Hotronic"s most powerful and compact Battery Pack. There are three cells in each Battery Pack to ensure that your feet can stay warm for over 15 hours. The temperatures can vary between 83 degrees and 144. . Model Year: 2014, Product ID: 252777, Model Number: 1157, GTIN: 7640121730542