Warmly in Sweden, the company that markets the unique hand warmer, gives the following answers:
The hand warmer's content consists of rechargeable lithium batteries and produces heat through heating coils.
By pressing the "on" button on the hand warmer, it is activated and quickly heats up.
The temperature rises to about 40-50 degrees and remains at that level for 5-8 hours before it gradually decreases.
To reactivate the hand warmer, it is simply recharged through a USB into a standard adapter.
The hand warmers can be reused hundreds of times, at least.