Boating Tips


Posted 9/18/2009

It's best to have two battery systems on your boat.  Fig. 1  Make sure to securely fasten the battery to the boat.

Outboard-powered boats can consume an incredible amount of electricity, with all the electronics, lights, trolling motors, windlasses and blow-your-mind sound systems swilling electrons like vampires on spring break – and that doesn't even include the juice to start the engine.

So where does all this power come from? The batteries in the boat and the outboard's charging system. Think of the batteries as electrical repositories that store the electricity until it's needed, and the engine's charging system as the batteries' benevolent partner that refills the batteries as they operate. (This is the condensed version; there's actually more to the process, but you get the idea).

Feed Me
Most outboards need electricity to power the electric starter, the computerized engine management systems (electronic fuel injection, ignition timing, etc), as well as the power trim and tilt functions.

Now factor in all of the electrical devices on the boat – navigation, cockpit, and cabin lighting; bilge, livewell, bait well and wash down pumps; electronics (GPS, radar, chartplotter, fish finders, VHF radio); trolling motors; trim tabs; and tsunami-inducing mega-amplified weapons of mass entertainment – you're going to need a lot of juice to keep everything going.

Battery Selection
We strongly recommend two battery systems – a dedicated cranking battery to make sure that the engine starts when it's time to head home; and at least one "house" battery for the boat's electrical devices (trolling motors may need two or three batteries, depending on the size of the trolling motor).
The battery used to start the engine should be a marine cranking battery; however on smaller boats that use only one battery, a combination cranking/deep-cycle battery should suffice, provided it meets the specs for your engine.

Minimum cranking battery specifications are established by the outboard manufacturer and are usually in the engine's owner's manual. These specs include Cold Cranking Amps (CCA) @ 0°F, Marine Cranking Amps (MCA) @ 32°, and Reserve Capacity (RC) Minutes @ 25 amps of electrical draw. But remember, the numbers in the owner's manual are the minimum amount of power that your outboard needs. You might want to invest in a cranking battery with the highest ratings available that will still fit in your boat's battery box.

Deep-cycle batteries are ideal for supplying energy to the boat's electrical system, because unlike cranking batteries that deliver short bursts of power, then get recharged by the engine's charging system, deep-cycle batteries provide a constant flow of electricity for extended periods of time until they're almost completely discharged; just recharge 'em and they're ready to go – for hundreds of times (or cycles).

There aren't really any established minimum requirements for deep-cycle house batteries; you'll need to figure out how much electricity your boat needs and buy the batteries accordingly. It's not as hard as it sounds – we've provided a simple chart to help you in your calculations – see figure 1.

Charge It
Your outboard's charging system can recharge more than one battery during the course of a typical boating trip. But how does the engine know which battery to send the electricity to?

Yamaha offers a Battery Isolator System to help make sure the cranking battery isn't depleted by the boat's accessories (which could happen if the house battery was low on juice – the accessories would then rob energy from the cranking battery.

Here's how the Yamaha Battery Isolator System works: after the engine is started, the battery with the lowest charge receives most of the charging system's output. When both batteries have been brought up to the same charge level, each battery gets equal amounts of electricity from the outboard's charging system.

Boats with several deep-cycle batteries may need an auxiliary charger to maintain the batteries at an optimum state of readiness.

Securing Your Batteries
Marine batteries come from the factory with wing nuts on the small terminals, but it's a good idea to replace the wing nuts and fasten your boat's wiring to the terminals with stainless steel hex nuts and lock washers. If you use these stronger fastening devices, the batteries are not as likely to work loose when the going gets rough.

Other Considerations
Mount batteries away from fuel system components (gas tanks, fuel lines, etc), and make sure each battery is securely fastened to prevent it from bouncing around and creating a potentially dangerous situation.

Electricity doesn't have to be intimidating or mysterious; use your head; do some research ( is a great resource) and ask your local dealer lots of questions – the more you learn, the more confident you'll be.