depth locator

Today i was on the water fishing, and was motoring along about 2-4 mph and had my trolling motor in the water, a message popped up on my deepthI/fish locator and it said "voltage high" was only on for a sec and went off,this has never done this before and i have had the locator for many years. The only thing i have done was put a circuit breaker
on the trolling motor battery in the last couple of days, i am not sure if the locator runs off the trolling battery or the cranking battery you fellas got any ideas. If so what does it mean