https://myastroshop.com.au/products/...earchCat=Brand
I had 2 of these running all night off a clapped out old Supercheap Auto jump starter pack. Had them on the low setting. One behind the objective cell, one on the guidescope objective.
By 1am everything around was covered in ice and frost (lens caps, bahtinov, neoprene computer cover, rug I put the power cable on the ground etc. Not a zot of ice or dew on the glass or the tubes. NADA.
Cheap, and don't need a separate controller, as the controller is built into the cable - low, off or high. NEVER had to go high yet, and it was -4° last night.