Therm-ic Battery Packs!
If you have pre-installed heated insoles in your boots, (you'll know this by the wires coming out of the back of your boots) you'll need batteries to power your heat.
So what's the difference in batteries? All Therm-ic batteries produce the same amount of heat. The difference is how long the heat will last. The more expensive the battery, the longer the battery will last. Also, some have added features like a remote control or use a phone app to control your batteries.
Be careful which battery system you order. 2017 and older insoles have a 4 pin connector and WILL NOT WORK with the new C-Pack batteries.