Originally Posted By: expat
Our neighbour has a tow horse trailer, it gets little use but she does get in maintained.
The is a small 'motorcycle' type battery near the hitch that seems to be left untouched for many years.
What is the function of this battey?
Probably power for the breakaway brakes. There should be a switch near the tongue that would have a lanyard and a pin, the idea being if the trailer came loose from the trailer hitch, the lanyard would be attached to the tow vehicle so it pulls the pin, and the battery applies the electric brakes. If the trailer has electric brakes, it's usually required to have a breakaway switch and battery.