MaySpare 12V 140Amp Voltage Sensitive Relay VSR Double Battery Automatic Charging Relay Dual Smart Battery Isolator

what's the override for?

Boat use. Off-season how do I keep both batts charged/ maintained? 1 or 2 bank charger if both vsr post are sensing? Most others have a + trigger wire

what is the yellow wire and how is it connected is a switch included?

Can this be used to supply power to the aux terminal on a 7 way connector of a tow vehicle even if the trailer has no battery but has interior lights?