(on my current boat)
My Lowrance units have always been run off the trolling motor battery, no probs !! That was originally a Elite 5DSI, then a Hook 5", and now the Hook 7. My current Garmin 93sv/Livescope setup is run off a separate battery (solely for that setup).

On previous boats, the console units were run off the starter battery ... and probably so were the bow units. But those units were on the boats at the time of purchase. They were all the simple b/w 2d units.