The Telrad Heater helps to eliminate condensation from your Telrad Finder.
0.16 Ampers at 12 Volts
You would also need to have a dew controller or similar product to use it.
This is an original Telrad product.
Image: Telrad Heater installed on a Telrad Finder on a 10" Skyliner Dobsonian telescope.
A wide range of accessories and replacement parts for your Telrad finder are available from 365astronomy.