This is a pair of the 120cm Extension Cords. They are compatible with the Power Plus and the prior battery packs and insoles. Extension Cords permit clipping the Battery Packs to the waist (80cm) or the chest (120cm). The cord is run underneath the pant leg, and plugs into the heater cord.
This does several things:
1) It keeps the batteries warm for a longer heating period.
2) It allows you to turn them on and off (or change the setting) without bending over i.e. on a chair lift or in a tight line.
If you use them for fishing, the 120cm length allows you to put the batteries at the top of the waders.