Many of the designs use automotive diesel glow plugs as the heater. Some I have used are only rated for 11 volts continuous and this is with the body screwed into a solid heat sink. They are on the ragged edge at 12 volts so I sure would not recommend them across two 8V batteries in series. Hooking in parallel will not increase the temperature.
Not sure if this is the best place to post this, but I have a modification to a cheap vaporizer I bought off of ebay that others might like to use. My Lang hives have screened bottoms so they need to be closed for OA treatment anyway.
My modification is I used high temp RTV to attach the bottom of the vaporizer to a piece of cementboard siding that I had leftover from a chicken coop project and also attached the metal/foam insert that closes the entrance to the siding. Note: this is cement siding, so only about 1/4 inch thick or less not cementboard backing which is thicker.
I cut the siding to fit the inside dimension of the bottom board except it closes the entrance when about 1/4 inch from the back wall (it is sitting on top of the wooden lip at that point).
It isn't air tight but seems to close the hive up pretty well without needing rags or the like. The cement board doesn't burn. You have to slide it in slowly so the girls can get out of the way, but otherwise pretty simple to use.
Hope someone else can use this idea.
To be clear, the cement board goes in the entrance and sits above the screen. It does not slide into the slot for a sticky board.