I bought this to add a little heat to a sleeping bag for a pending fishing trip into the Northwest Territories. I have not used it for that purpose, but I have tested it to see if it should work out.I am satisfied that it will, and that it will be GREATThe picture is of a test in the works.A bit of background. I am testing a 10,000mah battery, borrowed from a VOLT heated vest, and how it will work out. 10, 000 ma is, of course, 10A. Remember that Amps(A) multiplied by Volts(V) equals Watts(W). You need to know, as well, that a standard battery pack gives 3.7V at all times. A 10,000mah battery will give 10 amps for one hour (=10,000mah, thus the “h” in “mah”). Or it will give 1 amp for 10 hours or any combination that multiplies to 10Ah.At 3.7V that means that the capacity of the battery is 37WA , ie., it will give some combination of amps and hours, always at 3.7V, such that the product of the three is 37.Testing the pad and battery.On low(green) my 10,000mah battery (=37WA as described above) was used up in just under 6 hours. The meter showed total consumption of about 32 WA. Plainly either the battery was not fully charged or it is not efficient to a full 37WA, or a bit of both. On low heat(green) it used about 5.4WA.On a similar test, on high heat(red) it consumes about 9.6WA. So in theory, the battery should be good for about 3.8 hours. I got more like 3.2.The picture is testing on medium(blue). it shows power consumed and time passed. It looks like it is using about 6.8AH. So, ideally, it should be good for 5.4 hours before the battery is fully discharged. More likely, given that this battery is not giving a full 37WA, I expect to get about 4.7 hours. If I get something different, I will amend this reviewIn summary, total capacity should be 37, actually less, maybe 34. Low=5.4, medium=6.8, high=9.6 So some time at low, medium and high at their consumption rates for the time used will work at out so long as the total use does not add up to more than 34My experience is that to have the battery go dead after about 5 hours sleep works out well. The residual heat stays until it is time to get up. YMMV.The pad gives of a warming factor. It is not meant to be a sole source of heat. It just takes the chill off a cold night in a sleeping bag and lets you sleep without any cold effect.I think a 10,000mah battery will be enough. Of course, 20,000mah would be betterI hope this helpsAddendumI’m back. It was cold up north this year. I was glad to have the padThe battery worked but a 20,000ma one would be better in that it could warm the sleeping bag before getting into it then running on lowQuite happy with it after the ideal test for my needs