• Should my boat be rigged with a starting or a deep cycle battery, and why?
• I'm seeing a small spark when I connect the battery cables. Is this ok?
• How do I charge two batteries with my outboard motor?
• How do I hook up a tachometer or other gauge to my outboard motor?
• What do the warning horns indicate?
• What is the correct battery for my outboard motor?
• What are the general wiring colors used on Mercury outboard engines?
• What is the correct tachometer setting for my outboard motor?

Should my boat be rigged with a starting or a deep cycle battery, and why?

There is a difference between an ordinary starting battery and a Deep-Cycle battery. Starting requires a high amount of energy for a short period of time (about 30 seconds maximum). Only a small amount of the battery's capacity is used. Once the engine starts running, the battery is recharged quickly by the charging system.

A Deep-Cycle battery supplies a relatively low amount of current for a long duration. Deep-Cycle batteries, unlike starting batteries, can be run down and recharged repeatedly with minimum loss of capacity. Deep-Cycle batteries are designed to power electric fishing motors, and other electrical accessories in boats and recreational vehicles such as radios, TVs, fans, etc.

Since starting batteries and Deep-Cycle batteries are designed for different purposes, they are constructed differently inside. Starting batteries have porous active material. The plates are thin and are designed so the high-amp energy can be quickly delivered for maximum starting power. Repeated cycling, which involves lower capacity drains and recharges, weakens the positive plate. The active material drops from the grid, thus, in repeated deep discharge/recharge applications, the capacity of the starting battery drops below desired levels in about 50 cycles.

The Deep-Cycle battery has a denser active material and thicker plates to withstand deep discharge/re-charge service.

I'm seeing a small spark when I connect the battery cables. Is this ok?

Yes, newer engines require a small reference signal.

How do I charge two batteries with my outboard motor?

Using an outboard to charge two batteries is only effective if the outboard charging system is capable of delivering more than 15 to 20 amps. One point to remember: most systems are rated at wide-open throttle and charge substantially lower amounts at slower engine speeds.

Engines equipped with belt driven alternators and some smaller outboards can use a battery isolator to direct current to each battery. The isolator allows one battery to be discharged separately from the other and still allows both to charge from a single source. Carbureted and EFI 2.5L outboards are equipped with a dual regulated charging system. This system can be split, allowing half of the system to charge both batteries.

Other options may be available, contact your local Mercury or Mariner Outboard dealer for additional information.

How do I hook up a tachometer or other gauge to my outboard motor?

Each Mercury Precision Part gauge contains instructions on how to connect the instrument. Our service manuals contain similar information and are available through a dealer or from the publications department at Mercury Marine. Use the Bookshelf link on the Mercury Dockstore page if you need to place an order for a service manual.

What do the warning horns indicate?

The warning horns vary model to model. Generally a solid tone indicates a problem that can cause immediate engine damage and the engine should be stopped. An intermittent tone indicates a problem that will not cause immediate damage but the operator should inspect the engine as soon as possible*. Refer to your Operation, Maintenance and Warranty Manual for detailed information concerning the warning systems for your engine. Use the Bookshelf link on the Mercury Dockstore page if you need to place an order for a service manual.

*On 135 HP (2 litre) through 200 hp (2.5 litre) V-6 models, an intermittent warning horn may indicate a problem with the oil injection system, engine should be stopped and inspected as outlined in your Operation, Maintenance and Warranty Manual.

What is the correct battery for my outboard motor?

Battery Ratings Note: These are minimum engine specifications. Additional electrical loads from the boat will require larger batteries.

What are the general wiring colors used on Mercury outboard engines?

What is the correct tachometer setting for my outboard motor?

* Use QSI tachometer, other models require engine wiring harness changes.