1.First of all,our size is the width of the heat shrinkable tube:so the heat shrinkable tube has a circumference that is twice the size.
2:Calculate the perimeter of the battery pack
（https://ae01.alicdn.com/kf/H39027923be614258961a4b90b465ca77a.jpg）（https://ae01.alicdn.com/kf/H6fc9e806387f4e2eaffb545c21cf3f97E.jpg）