The Therm-ic Powerpack SuperMax+ with Perform insoles can be your best choice because it's easy to install and the batteries can be recharged up to 1,000 times.

Therm-ic SuperMaxMax+ features......

• Rechargeable 1900 nickel metal hydride batteries. If you are using heat a lot, rechargeable batteries are less expensive than AA batteries!

• Quick and easy installation! Thermicsoles already have the heating elements built in. All you need to do is remove your current insoles, trim to size, install in boots, plug in and turn on. Fits all types of winter boots.

• Impulse Control- The warmth is transferred from the battery pack to the heating elements by impulses which deliver more energy than a constant power on used with other brands.

• Comfortable warmth up to 20 hours with freshly charged batteries.

Select between 3 settings to determine the amount of heat you need.

• Level 1 settings: 37°C or 99°F for up to 20 hours

• Level 2 settings: 45°C or 113°F for up to 8.5 hours

• Level 3 settings: 70°C or 158°F for up to 4 hours

Results are based on freshly charged batteries. Keep in mind, you don't have the heat on all the time, only when you need it. For instance, you turn the power off when you go inside for lunch or if you are not cold.

You'll receive;

• Instructions on how to use.

• 2 1900 nickel metal hydride battery housings each with 3 heat settings and clip on the back of a boot and can be recharged up to 1,000 times.

• 1 GLOBAL battery charger that can be used in North America, UK and Europe. Estimated charging time is 4.5 hours. You can use the charger in other countries with a power converter. Includes an automatic charge-discharge recognition.

• TWO Perform insoles which are anatomic 3D shaped insoles with connecting wires. The Perform insoles give great support for stability and balance. They are made of high quality EVA foam. The heating elements are built into the toe area of the insole so all you need to do is remove your current insoles, trim the Perform insoles to the same size and slide the Perform insoles in. You can opt to run the wire for the battery right up the back or put a small slit in your boot liners and run the wire between the liner and shell. (We recommend the later.) It took us less than 30 minutes to install.