Check out https://handybobsolar.wordpress.com. He gives really good explanations about solar and answers your question and more. Was a huge resource for my solar needs.
They are timer switches for different outlets. One for the electric cooler, one for the floor fans from the cab to the living space, and the last for an outlet near my bed to cycle my mattress heating pad and electric blanket. Everything is 12V DC.
I just wanted to say hello and introduce myself as I have recently become a vandweller. Been reading the forum and blogs for a bit while spending nearly the last five months converting a Ford E350 extended cargo van. My plan for now is the stealth variety with weekends out of town as I am stuck...