Battery; Battery Precautions For Multiple Engines - Mercury 4.2 Diesel Operation & Maintenance Manual

Section 4 - Maintenance

Battery

Refer to the specific instructions and warnings accompanying your battery. If this information is not available, observe the
following precautions when handling a battery.
Recharging a weak battery in the boat, or using jumper cables and a booster battery to start the engine, can cause serious
injury or product damage from fire or explosion. Remove the battery from the boat and recharge in a ventilated area away
from sparks or flames.
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 Module (ECM) and Vessel Integration Panel (VIP). The ECM and VIP require 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 drop below the ECM or VIP minimum voltage requirements. The alternator on the second engine may also start
charging, causing a voltage spike in the engine's electrical system.
In either case, the ECM could shut off. When the voltage returns to the range that the ECM requires, the ECM will reset itself.
The engine will now run normally. This ECM shut down usually happens so fast that the engine just appears to have an ignition
miss. Intermittent or temporary VIP shutdown can cause a loss of instrumentation, engine misfire and can adversely effect
power package performance and boat safety.
Batteries. Boats with multi‑engine electronic control power packages require each engine be connected to its own battery,
ensuring that the engine's ECM 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.
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90-8M0113988 DECEMBER 2015
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