In the event that the stereo has been functioning when the boat is not ON and running, the voltage drain on the battery (or batteries) may result in difficulties with restarting the boat. It may also cause intermittent erroneous or fluctuating gauge readings. When the voltage level reaches 10.5 volts or below, the system will shut o the stereo and sound the alarm. 

Operation 

Generally, the appropriate action is to leave the stereo OFF, as well as disengaging any other peripheral electrical components, and keying ON the engine. Running the engine at a moderate rate for several minutes without the additional drain of stereo and unnecessary electrical equipment will allow the alternator to recharge the battery or batteries, unless the battery(ies) have been used to the extent of their life span.