I just purchased a second unit. My first one was a gift and didnt come with a power pack so I used it in the house while plugged into my phones wall charger via a USB cord. Im a avid gardener living in Central Texas where the summers are sweltering. Last summer I would garden in the heat as long as I could stand it then go in the house, collapse into my recliner and place the mini cooler on my wrist, my jugular, the back of my neckanyplace where blood vessels ran close to the skin.all the places I used to place an ice pack. The mini cooler cooled me off quickly just as if I was using an ice pack but it doesnt drip water down my neck and make a mess the way an ice pack does. It gets super cold in a matter of seconds and stays cold as long as its attached to a power sourcewhich for me was forever since I was plugged into my houses electricity via my phone charger.
One time I was using it on my wrist when I realized it wasnt cold any longer; I couldnt feel it cooling my wrist. I pulled the device off my wrist, touched the cooling plate and it was ICE cold. At that point I realized my wrist was numb. It had been on the cooling plate so long Id lost all sensation on the surface of my skin. THAT is a good cooling device!!! Now with the power pack, I anticipate my mini cooler will go with me anytime I have to be outside for an extended period during the oppressive Texas summer. It has a forever place in my life. Great device! Definitely 5 Stars.