posted 04-15-2014 10:03 AM ET (US)
In the past--really the ancient past--some devices for music reproduction with loudspeakers that incorporated a receiver for the AM or FM Broadcast bands needed to be constantly connected to a source of 12-Volt power in order to maintain stored data in memory, such as preference for stored memory channel frequencies, and those devices often came with instructions about connecting them directly to a battery without any sort of intervening shut-off switch.In a modern small boat, there is no good reason for any device to be connected directly to the battery if the boat has good primary and secondary power distribution. Advice in installation manuals written by product manufacturers tends to presume their wiring has some sort of priority over all other electrical power wiring. Adhering to that advice tends to result in poor wiring practice and sloppy installations. I would ignore it.
Connect any electronic device load on your boat to a branch circuit in your secondary power distribution, using a branch circuit that is protected by an over-current device of appropriate rating for the wiring and load. If the device cannot tolerate being disconnected from 12-Volt power without losing important presets, return the device and get something more modern.