The product is really good. If you use it in gloves or in socks, it becomes nicely warm :) I tested two pads with a 7000 mA/h battery and it took 1,5h until the battery was empty which is ok I think. Always bare in mind, it is very inefficient to convert electric energy into heat so 1,5h is good. :)
I received 4 heat pads. I tested them with 3 different power source but none of them is working. Poor quality. Waist of money. Seller does not want to help.