Active Apparel
Halve the element resistance for twice the heat and the battery empties twice as fast. Duty cycle is the only free lever.
— h
Hours of heating at the chosen duty cycle
Runtime uses nominal capacity at nominal voltage and will overstate cold-weather performance, which is precisely when the garment is used — lithium cells lose a substantial fraction of their usable capacity near freezing, and the pack voltage sags under load, reducing power as well as duration. The temperature rise is a whole-garment steady-state average and says nothing about local hot spots at the element itself, which is where burn risk and fabric damage live. Any heated garment needs over-current and over-temperature protection and should be built and tested against the applicable electrical safety standard.
Heated Garment Joule Heating Battery Life & Wattage — free, with the formula and a worked example, at Textile School.