I sell battery powered gloves because it is based on the principle that as long as there is a source element keeping your body temperature up you will stay warm in the cold. This can be done not only with battery powered gloves, but with a warm tea, and heated pads.
You can be confident that you will be warm even when you accidentally underdress, because the heating element is adding a higher technology to you wear.
In the local store you can find battery powered gloves for $250! Ours go for a fraction of what you can find in retail. Oh, the glory of online shopping.