dew heaters

[Raymond Locke]

Does anyone know how to make/reguate a dew heater for a Celestron 9.25?  I dont mind spending 80$ for the heater but not $500 for a controller and power supply??
My plan is to buy the ring dew heater from Celestron or HIgh Point and run it to a small 12vdc power pack of 2.8MAh.  I could put  one of my a variable resistors in line to control the voltage.

Any other suggestions as to how to control dew?  I do have and use the long dew shield.