Choosing a Battery

September, 2019

Marine batteries are the unsung heroes of boat accessories. They stay hidden in a dark compartment, mostly ignored by everyone onboard, as they quietly do their jobs. That is, until the engine fails to start or the trolling motor doesn’t work.

The truth is, next to fuel, the batteries are the most important marine accessories on your boat. Some boaters give little thought to choosing the right batteries for their boat, though. After all, a battery is a battery, right?

Not necessarily, and here‘s why. Today’s more powerful accessories—such as widescreen electronics and high-thrust trolling motors—consume more amps than ever. The good news is newer batteries offer longer battery life, lighter weight and other features.

Do you need a deep cycle, starting battery or both? You can also have more choices than lead acid batteries. There is AGM, gel and lithium ion—each with its own pros and cons worth considering.

If your crusty old battery needs to go, find a replacement at your nearest Bass Pro Shops or Cabela’s. You will also find friendly, expert advice on which batteries are best for your boat.

Before you go, get started with these helpful tips.

Know the basics
What size battery do you need? Measure the battery compartment and check the Group Size, which is the industry standard for the physical size of batteries. Here’s what else you need to know about the basics of battery selection.

For starting batteries-the most important feature to consider is cranking amps (CA). That is the discharge load that a fully charged battery can provide in 30 seconds. That’s about the time a battery needs to be at peak performance to start the engine. The owner’s manual or your dealer can tell you how much CA is needed for your boat.

For deep cycle batteries—those used to power all your onboard gadgets throughout your outing—you need to consider amp hours (Ah). That is the amount of energy charge that will provide one ampere of current flow for one hour. You can do the math for how many amps you need using this example—a battery rated for 100 Ah at 20 hours can discharge for 20 hours with a 5-amp load. Knowing how many amps you need is very important with today’s high-powered, amp-thirsty electronics.

Amps are important, and so is the reserve capacity (RC) of the battery. That is the number of minutes a fully charged battery can manage a load of 25 amps before falling below 10.5 volts at a given temperature. RC is like the backup, or reserve power, for batteries designed for deep discharge, like those used to power accessories.

Beyond those basics, avoid mixing and matching battery types or brands throughout the electrical system. The battery charger will operate more efficiently as a result. Also, replace all batteries in a system at the same time. If you don’t, the older batteries in the bank will place a drag on the newer batteries, shortening their life span.

Lead acid
Lead acid batteries have been around as long as the engines used to power them. Find them in automobiles, boats and just about any other machine needing an electrical crank.

Pros: They can’t be beat for their cost per watt. Inexpensive, reliable and effective.

Cons: Can be high maintenance when compared to the newer types. They are more fragile. Internal damage can result on hard impact.


AGM
Absorbed glass mat (AGM) batteries contain electrolytes in a woven roll of fiberglass. That prevents the electrolytes from spilling, even if the battery housing is damaged or turned upside down.

Pros: No terminal corrosion because acid is not used. Higher CA and RC rating. Quicker and longer-lasting charges than lead acid batteries.

Cons: Overcharging can shorten life expectancy. Need to keep charged to at least 50 percent capacity for best performance.

 

Gel
Gel cells use a blend of sulfuric acid and silica to create a fixed gel-like substance. The immobilized gel means they don’t need to be mounted upright.

Pros: Sturdier and can withstand hard impacts, e.g., pounding waves. Holds deep cycle charging longer than other batteries.

Cons: Need a specific charger.

 

Lithium Ion
You have a smaller version in your cell phone. Lithium ions transfer electrons at each end of a cathode and anode.

Pros: Up to 70% lighter than lead acid batteries (think improved fuel economy and engine performance), more environmentally friendly and have longer lifespans.

Cons: More expensive than other types of marine batteries. Slower charging. 

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