Poor performance in cold conditions
Bought one of these for playing golf as I have arthritis in one of my hands. Charged the hand warmer up to full and after only 4 holes ( 1 hr ) the thing was dead. Their documentation states that the estimated working time is based on tests done at 25 deg C !! Who needs a hand warmer at that temp !! I was using mine when the temp was approx 4 deg so think before you buy.