Boat Battery Maintenance

Boat Battery Maintenance


You’d think most anglers would be obsessed with the health and well-being of their boat batteries. After all, we rely on batteries to start our outboards and run a wide array of on-board electrical accessories, including trolling motors, sonar units, GPS units, livewells, baitwells, bilge pumps, navigation lights and VHF radios. In reality, though, most of us forget about our batteries once we’ve hooked them up. About the only time we otherwise give them any thought at all is when the gremlins come calling-and by then it’s often too late to do anything to fix the problem.

Little wonder that experts such as Dave Duffin, Minn Kota Canada’s sales manager, and Ian Cummer, Mercury Marine’s technical account manager, say boat batteries are the single-most neglected piece of equipment in the average angler’s boat. So what exactly should an angler do to keep those annoying battery gremlins at bay? To find out, we asked Duffin and Cummer for their expert advice.

1. Know Your Batteries

One way to beat the battery gremlins is to know the difference between the two types of marine batteries. Although cranking and deep-cycle batteries may look identical on the exterior, their internal construction, as well as their purposes and functions, are as different as night and day.

Think of a cranking battery as a racehorse and a deep-cycle battery as a Clydesdale. Cranking batteries are designed to deliver an instant burst of energy to start your motor, then to rest and recuperate. Deep-cycle batteries, meanwhile, are designed to deliver power more consistently over an extended period of time to electrical accessories, such as trolling motors. Most larger fishing boats will have at least one of each type of battery on board-a cranking battery to start the main engine and a deep-cycle battery to power the electrical accessories.

What accounts for the difference between the two battery types, says Duffin, is the way they’re constructed. “If you remove the casings,” he explains, “you’ll see that a cranking battery has many more lead plates inside, so there is maximum amount of plate surface area. But the plates are thin. The plates inside a deep-cycle battery, on the other hand, are much thicker and coated with different materials, allowing them to accept and deliver a large amount of current over a long period of time. It also means deep-cycle batteries can survive numerous cycles of charging and discharging. Starting batteries are not designed to do this. In fact, you can only draw them fully down a half-dozen times or so.”

The message here? Don’t hook up your trolling motor or other electrics to the cranking battery, or you’ll quickly ruin it.


2. Avoid Sulphation

According to Cummer, marine batteries should last 48 months, but three out of four never survive that long. Some fall prey to gremlins because of the added power demands we place on them, while others fail because of a lack of simple maintenance.

“Sulphation is the biggest culprit,” Cummer explains. “It occurs when sulphur molecules in your battery’s sulphuric acid electrolyte begin to coat the lead plates. It’s like plaque building up in your arteries. The coating continues to thicken until the battery fails.” Now, we all know that a steady diet of french fries, burgers and onion rings will clog arteries, but what causes sulphation?

According to Cummer, sulphation can occur if you don’t keep the battery’s electrolyte level topped up so that the battery plates are completely submerged. If they’re not submerged, sulphur molecules will immediately start to coat any exposed portions. To prevent this, keep the electrolyte level topped up with distilled water (never use tap water).

Sulphation can also happen if you don’t fully recharge your deep-cycle batteries as soon as you return from fishing. “Every minute you delay contributes to sulphation,” says Duffin. “And not fully charging your batteries heightens the predicament. A fully charged battery inhibits sulphation. So if you only recharge it to, say, 80 per cent of its capacity, you’re giving sulphation a 20 per cent opening to attack your battery.”

3. Mind the Temperature

Extreme temperatures are sure to attract battery-killing gremlins. During the cold of winter, for example, the chemical process that produces electricity inside your battery becomes repressed. For this reason, it’s critical to ensure your batteries are fully charged in the fall before you put your boat to bed and that you periodically check that they remain charged over the winter.

Gremlins also thrive under high temperatures, which can lead to what Cummer refers to as “internal battery discharge.” Park your boat inside a garage for any length of time during a summer heat wave, for example, and your batteries will quickly weaken, even if they’re brand new and fully charged. You can help prevent this by opening the battery box compartment in your boat so the battery doesn’t bake, or by parking your boat in a cooler location, such as under the shade of a tree.

Keep in mind that a fully charged, well-maintained battery—even when disconnected and stored properly—will still discharge itself naturally. The rate of discharge will vary with the temperature: faster in warm weather, slower in cold (the ideal storage temperature for marine batteries is 0°C).

4. Choose the Right Type

Duffin says to keep three things in mind when selecting a battery. First, make sure you buy the type of battery you need, be it a cranking or deep-cycle battery; then find out when the battery was made; and, finally, check the battery’s reserve capacity, or RC.

Whether you choose a cranking or deep-cycle battery, the date will be stamped somewhere on the outside case. Just remember, the older a battery is, the longer it’s likely to have sat on the store shelf, which means it likely hasn’t been charged and sulphation has probably begun.

You’ll also find a battery’s RC rating (also referred to as “amps hour rating”) listed on the casing. That tells you how long (in minutes) the battery can supply 25 amps when it’s fully charged and the temperature is 27°C. Duffin says anglers should always buy deep-cycle batteries with the highest possible RC; 180 minutes is best. Also, avoid inexpensive batteries, as they tend to have lower RC ratings. When it comes to cranking batteries, RC isn’t quite as important because they get used much less. Still, you’ll want to buy one with the highest available rating.

When choosing a cranking battery, just be sure you’re comparing apples to apples. According to Cummer, today’s high-performance outboards require a minimum of 1,000 cranking amps; you can find the exact number for your motor in the owner’s manual. Confusion can arise, however, because some batteries specify cranking amps (CAs) while others list cold cranking amps (CCAs). CCAs are the number of amps a battery will deliver for a 30-second period when the temperature is 0°C, whereas CAs are the number of amps a battery will deliver when the temperature is 27°C. Given our cold climate, and the fact that much of the best fishing occurs in the spring and fall, it’s wise to opt for a battery that specifies CCAs.

5. Keep It Charged

After pure neglect, improper charging probably accounts for more battery failures than anything else. Most cranking batteries are recharged by the outboard, the same way a car engine recharges the car battery when you’re driving. That said, it’s always a good idea once or twice a season to recharge your cranking motor, just to make sure it’s fully charged so you don’t get stuck out on the water.

As for deep-cycle batteries, more and more boats today have built-in chargers. Just plug in the cord at day’s end and the charger does the rest. If your boat doesn’t have a built-in charger, buy a portable one that’s capable of recharging deep-cycle marine batteries. To extend the life of a new battery, draw it down sparingly and recharge it as soon as possible after the first few times you use it.

It’s best to recharge deep-cycle batteries slowly, typically overnight. For that reason, 10- to 20-amp chargers are standard. You’ll want one with an automatic shut-off feature. That way, if you forget to unplug it, the gremlins won’t be able to boil away the electrolyte and fry your expensive battery.

Some higher-priced battery chargers will allow you to keep the batteries hooked up for extended periods of time, even after they’ve been fully charged. If your charger doesn’t have this feature, or if you’re not sure whether it does, disconnect it. As for the newer gel and absorbed glass mat batteries, some require special charging protocols. Be sure you’re familiar with them if you use those types of batteries.

Whether you need a cranking battery to start your outboard engine or one or more deep-cycle batteries to power your electric trolling motor and other electrical accessories, the bottom line remains the same: purchase the freshest batteries you can find with the greatest amount of RC available. And then look after them with the same great care you would any of your other important pieces of fishing equipment. If you don’t, you’re sure to see those troublesome battery gremlins rear their ugly heads, over and over again.

Stay Connected

Should the gremlins prevail and you end up needing to borrow a cranking battery to fire up your outboard, take care. Back in the days when technology was much simpler, an angler would often unhook the borrowed battery and return it once he got his motor running. These days, though, that’s a big no-no. “All of the sensors and computers inside today’s modern outboard motors require a minimum amount of battery power, even when the engine is running,” says Ian Cummer, Mercury Marine’s technical account manager. “In addition, when you disconnect the battery cables you send a voltage spike throughout the engine, which can seriously damage the internal electrical components.” Bottom line: don’t do it.

Are You Getting Enough?

Before buying a new deep-cycle battery, make sure it offers enough juice to do what you want it to do. That means you first have to calculate how much power you’ll actually need over the course of a typical day of fishing. Here’s an example of how to figure it out.

Let’s assume your boat has a 12-volt, 40-pound-thrust trolling motor, which draws 42 amps per hour when it’s running at full speed (such figures can be found in the owner’s manual for your trolling motor). Most of us don’t operate our trolling motors that way, however. On average, we set the gauge for about half speed, which reduces the motor’s draw to roughly 20 amps per hour.

To keep deep-cycle batteries in optimal condition for as long as possible, they should never be completely drained of power, says Dave Duffin, Minn Kota Canada’s sales manager. He suggests building in a 20 to 30 per cent reserve factor, which, in this example, amounts to an additional five amps per hour. That makes the total electrical need approximately 25 amps per hour.

Of course, if additional electrical accessories, such as a bilge pump, sonar unit and livewell, are drawing from the same battery, each item will add to the power requirements. (Duffin recommends making a list of all the accessories and calculating their total amp draw.) But to keep things simple for the purposes of this example, assume we just need the 25 amps per hour to power our trolling motor.

Now check the chart below to find out how many minutes of running time, or discharge time, that 25 amps will allow (most battery manufacturers provide these charts). As you can see from this example, the MK 20 battery will power the trolling motor for 180 minutes. To figure out how long your battery will power all your electrical accessories, you’d simply total the amp draw of each accessory and compare it with the chart.

Many keen anglers probably feel that three hours of trolling isn’t nearly enough. It may not be, but don’t forget that this is actual running time; most of us don’t use our trolling motors for more than 20 to 30 minutes each hour that we’re out on the water. The rest of the time we’re casting, drifting, netting fish, fidgeting with tackle or moving to a new location. So, based on the 20 to 30 minutes per hour we’re actually using our trolling motors each hour, that three hours of power should last for six to nine hours.

Still, some anglers may need more battery power. For instance, those who fish more than 10 hours a day in tournaments on big, open waters with heavy winds or in rivers with strong currents are forced to turn up the trolling motor speed (thereby increasing the power required) and/or use the motor almost constantly. If that’s the case, you may indeed need more deep-cycle battery power.

It’s possible to double the length of time the power will last by purchasing two identical 12-volt deep-cycle batteries and connecting them in parallel (see diagram on the right). Be sure not to mix and match brands or combine batteries of different ages, as they may interact poorly and damage each other. Otherwise, that system maintains the 12 volts of power while doubling the length of time it will last, which is sure to dampen the spirits of any self-respecting gremlin.

Anglers can also get more trolling time by buying a 24- or 36-volt electric trolling motor. Generally, higher-voltage trolling motors are more efficient and draw less power. Of course, to run a higher-voltage motor you’ll need to hook up two or three 12-volt deep-cycle batteries (two to run a 24-volt motor and three to run a 36-volt motor). In that case, the batteries would be connected in series. Again, gremlins beware.