A battery can lose 60% of its starting power when the temperature reaches 0-degrees F. Cold engines require more power from the battery at these temperatures. These two factors make it imperative that you use a battery wrap to extend the life of your battery, and assist in your cold weather starting requirements. Fully charged batteries have a significant drop in power at colder temperatures. The battery wrap allows you to have full cranking power regardless of the cold. The battery heater should not be used when the temperature is above freezing.