They do a great job of keeping hands warm
This was a gift for my sister but I love mine that I bought a year ago.
UPS lost the order and G-Tech customer service was all over it and replaced the order as soon as they found out. The battery functions as described and is the same model that comes with the hand warmer.
Battery packs are small enough to be out of the way and long lasting. All in all a great set up.
The second battery makes it possible for me to play 18 holes in pretty cold weather while keeping my hands warm. Great product.