I saw these in a shop.
10000mAh for 13.5 hours means a current of 0.74A. USB voltage of 5V would give a power of 5 x 0.74 = 3.7 Watts.
Here current is 5200mAh / 8 hours = 0.65A. That would give a power of 3.25 Watts. Not sure if these are valid calculations because of the voltage but 3W in an enclosed glove will have some effect.
