I would like to hook a solar panel up to the battery on my mighty mule gate opener, rather than spend all the beans on the "mighty mule" panel. The output on my panel on a sunny day at noon time in NE CT two weeks ago was approximately 20V DC, which is right where the branded panel is purported to be.

My question is whether there are electronics built into their panel that prevent overloading or draining of the battery; or rather, should I try to build a simple circuit to do this and if so is there someone willing to help me design such a thing? I can assemble and solder this I am sure, just don't know how to design what I might need.

I can provide more specific information to anyone interested in helping.

If the controller for the gate has solar marked terminals, you're most likely all set. Unless you have a huge solar panel putting out more watts than that controller is rated.

If no existing solar terminals you probably want to buy a solar battery charge controller and wire it up directly to the battery(s).

Thanks for the link, that looks like what I need; provided there isn't already such a circuit within the unit, which is a question I am trying to answer.

Looks like their control panels may or may not include connections for solar - some do, some dont. And if your's does have solar connections they apparently are only rated for a solar panel, or group of panels, up to 30 watts max.

I didnt spend much time looking and the model I looked at may not be identical to yours, so take what I say with a grain of salt about those contacts until you look in your manual & control panel.