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You should really use some form of a controller so you don't cook your OTA and draw too much power from your battery (or power supply)
The simplest controller works basically like a light dimmer on your home. Turn a dial to modify the average current to the heat strip. (variable length of pulses to the strip depending on dial position)
This method is a bit hit and miss as you may or may not dial the right value to keep the dew off the mirror or lens.
Dew will form on the surface when the surface gets below the dew point. So a controller that monitors both temperature and humidity, calculates the dew point and keeps the surface above the dew point is the best. This will save unnecessarily heating the surface creating unnecessary hot air turbulence and also reduce battery drain.
A compromise controller is one that measures the ambient air temperature as well as the temperature of the surface and strives to keep the surface say 3 degrees above ambient. The Kendrick Digifire FX Pro is an example of this type of controller. (and the long-promised Kendrick Premier Controller due promised now for mid-2021 is an example of a dew point controller)
Some telescope controllers/power systems, also have built-in dew controllers of varying capabilities. You can usually pick the type by the controls and sensors. If they have a dial, odds are it's a simple controller. If just a temperature sensor near the band and an air temp sensor, I'd guess an ambient temp control. If they also have a humidity sensor, then probably a dew point controller.
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