The Swiss website Fotichaestli sales USB lens heating pouches - I never knew such product existed, here are the details (Google translation):
Product information "Digital Camera Astro USB Lens Heater Warmer Strip for Telescope Scopes"
USB Lens Heater
Super fast and continuous warming with fast start up of 5 seconds to heat, and intelligently reach 50°C the maximum given the actual needs, while the average temperature stays at 30°C.
Protects the lens of your digital camera or finder scope from freezing by chilling fog and dew, enabling the devices to function properly at night when the temperature drops or places with bad weather.
Great idea for warming up water bottle, drink cup, feeding bottle or anything needs keep warm. Based on the USB port design, it is very handy to use because you can connect it either to your power bank or any other power source with a USB port.
With adjustable diameter and easy adherence, this dew heater strip fits to most size of telescope, finder scope, digital camera, bottle, cup, human wrist or knee. One heater strip to warm them all!
Can surprisingly be used as a special wrist strap/knee strap to protect them from cold weather or emergency low temperature condition, which the warmth goes through your whole body from where you attach.- Strip length: 37cm
- Strip width: 8.5cm
- Heater length: 7.48in
- Strip material: Neoprene and polyester
- Heater material: Carbon fiber heating coil
- Power Consumption: 5V 0.8A 4W
- USB cord length: 1.5m
- Velcro length: 12cm
