The switch will still work, but the brakes wont! The switch merely connects the electric brakes to a power source. You need a power source. You could use a motorcycle battery since you would at most make one stop, but you must have a source on the trailer. While connected to you tow vehicle, the battery in it will work the trailer brakes, but only while the umbilicle is connected. If the trailer gets loose the umbilicle will be disconnected. Welcome to the forums!
"Not all who are laundering are washed" say Bill & Heidi
'78 Excella 500,"The Silver Pullit". vacuum over hydraulic disc brakes, center bath, rear twin. '67 Travelall 1200 B 4X4 WBCCI 3737