Abstract: A multiple battery system and method for starting internal combustion engines, such as on a boat or vehicle, and for powering auxiliary functions that operate primarily when the engine is not running is disclosed. A first battery is used for starting the engine. A second battery is used to power the auxiliary features associated with the boat or vehicle primarily when the engine is not running. The first battery, referred to as the starter battery, is a high output battery that produces high bursts of energy for limited amounts of time. The second battery, referred to as the auxiliary battery, has a low power output over a fairly long period of time, is capable of being completely drained without harming the battery, and is capable of being fully recharged. The starter battery and the auxiliary battery are connected by a circuit that has an on/off switch controlled by an electronics control module. The auxiliary battery is always on line in the circuit.