MerCruiser 8.1 MAG, Owner'S Manual

Page: 85 / 152

Section 5 - Maintenance
90-864839070 AUGUST 2007 Page 77
Changing
Power trim fluid does not require changing unless it becomes contaminated with water or
debris. Contact your authorized Mercury MerCruiser dealer.
Battery
Refer to specific instructions and warnings accompanying your battery. If this information
is not available, observe the following precautions when handling a battery.
!
WARNING
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.
!
WARNING
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.
Multiple EFI Engine Battery Precautions
Alternators:
Alternators are designed to charge the battery that supplies electrical power
to the engine that the alternator is mounted on. When batteries for 2 different engines are
connected, one alternator will supply all of the charging current for both batteries. Normally,
the other engine's alternator will not be required to supply any charging current.
EFI Electronic Control Module (ECM):
The ECM 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 ECM's 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 ECM could shut off. When the voltage returns to the range that the ECM
requires, the ECM will reset itself, and the engine will operate normally. The ECM shuts off
and resets itself so quickly that the engine may only seem to have an ignition miss.
Batteries:
Boats with multi‑engine EFI power packages require each engine be connected
to its own battery. This ensures that the engine's ECM has a stable voltage source.
Battery Switches:
Battery switches should always be positioned so each engine is
operating off of its own battery. Do not operate engines with switches in 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 generators battery should be considered another engine's battery.