Therm-ic S-Pack 700 battery.

The S-Pack 700 battery has a maximum autonomy of 8 hours. It has three different intensity levels, allowing the user to adjust the level of heat to suit their needs. It can be recharged using the included USB charger.

The pack includes two rechargeable batteries. Easily adaptable to compatible heated socks to provide constant heating during winter outdoor activities.
In a nutshell

Pack of two S-Pack 700 batteries
Heating time level 1: up to 8 hours
Heating time level 2: up to 5 hours
Heating time level 3: up to 2 hours
S-Pack batteries are compatible with Therm-ic Powersocks
Pack includes a USB charger to charge both batteries simultaneously