Often when I am camping or when I leave my truck parked for a long period of time at home, I think it would be it would be nice to have the solar panel dump excess, unused power into the starting battery.

This means I would always have a very happy starting battery, ready to give maximum spin to the engine even in cold winter weather. The way to do this would be to have a voltage monitoring switch, like this $7 dollar XY-CD60 voltage-monitoring switch I got from AliExpress. For about twice as much, you can get also get it on Amazon. It came in the mail, and it looks just like below — I haven’t had a chance to test it, but it looks like it will work perfectly for my situation.

My plan is to use this “voltage switch” to connect the relay between the starting battery and other batteries charged by the solar to dump the excess charge into the starting battery. I will probably set the unit into out mode (discharge protection mode), with an activation voltage at around 14.0 volts, with a delay of maybe 120 seconds, so that the relay isn’t activated until I know I have a sufficient charge to keep the voltage from dipping back below the threshold when the starting battery connects. It will take a while to figure out what settings works well for me — I don’t want to connect the starting battery too soon and have the voltage drop have it shut off the relay prematurely.

The product didn’t come with any documentation but the AliExpress website has some decent documentation in somewhat broken English, but I think I’ll be able to get it working fine. I’ll let you know how it works out.