How long does a power bank heat a garment? Battery capacity, voltage and heating time of USB-powered heated clothing

Technical note explaining how the capacity of a USB power bank (mAh, at a cell voltage of about 3.7 V) converts into usable energy at 5 V (Wh) and into heating time for heated clothing, with worked figures for the Gløde 10,000 mAh and 20,000 mAh power banks (stated 3-6 h and 6-12 h for a heated vest, implying an average draw of about 5-11 W). Also covers what shortens heating time (heat setting, cold batteries, battery age, wind) and the 100 Wh air-travel limit. Published by Gløde B.V., glode.nl.