I have used this twice and both times it did not last more than an hour. I have not tried to charge my phone with it.
I’ve used this about five times now in winter conditions, snow and ice on the courses, the courses I play are hilly. Have used it when temps between 19 and 30 degrees. It takes longer to play 18-holes in these conditions, 2hours for 18 holes rather than 1:15 or 1.5 hours. The Innova Electric Handwormer, on the low setting (which I find to be plenty warm enough) runs out of power in about an hour and ten minutes. If purchasiung another handwarmer, I’d get one that lasts for 2+hours.