Mercury MerCruiser Diesel Inboard 2.8L Operation & Maintenance Manual page 76

Section 4 - Maintenance
Battery Isolators. Isolators can be used to charge an auxiliary battery used for powering accessories in the boat. They should
not be used to charge the battery of another engine in the boat unless the type of isolator is specifically designed for this
purpose.
Generators. The generator's battery should be considered another engine's battery.
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