Battery Precautions For Multiple Engines; Alternators; Engine Control Unit (Ecu); Batteries - Mercury TDI 3.0L Owner's Operation And Maintenance Manual

An operating or charging battery produces gas that can ignite and explode, spraying out sulfuric acid, which can cause
severe burns. Ventilate the area around the battery and wear protective equipment when handling or servicing batteries.

Battery Precautions for Multiple Engines

Alternators

Alternators are designed to charge a single battery that supplies electrical power to the individual engine on which the
alternator is mounted. Connect only one battery to one alternator. Do not connect two batteries to the same alternator unless a
battery isolator is used.

Engine Control Unit (ECU)

The engine control unit requires a stable voltage source. During multiple engine operation, an onboard electrical device may
cause a sudden drain of voltage at the engine's battery. The voltage may go below the ECU minimum required voltage. Also,
the alternator on the other engine may now start charging. This could cause a voltage spike in the engine's electrical system.
In either case, the ECU could shut off. When the voltage returns to the range that the ECU requires, the ECU will reset itself.
The engine will now run normally. This ECU shutdown usually happens so fast that the engine just appears to have an ignition
miss.

Batteries

Boats with multiple engine electronic control power packages require that each engine be connected to its own battery,
ensuring that the engine control unit has a stable voltage source.

Battery Switches

Battery switches should always be positioned so that each engine is operating off of its own battery. Do not operate engines
with switches in the both or all position. In an emergency, another engine's battery can be used to start an engine with a dead
battery.

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.
90-8M0145546 MAY 2018
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WARNING
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Section 4 - Maintenance
Page 85