What Type of Battery is a Marine Battery?

Are you cruising Australia’s Great Barrier Reef or day fishing the Andaman Sea out of Phuket, Thailand? Your boat needs reliable marine batteries. From open console fishing boats to long-distance cruising sailboats, boaters across the Middle East, Africa, Australia, and Southeast Asia place high demands on their boat’s batteries.

Knowing your battery options and what type of battery is a marine battery is essential. In this guide, we’ll look at the different types of marine batteries. And we’ll focus on the two most popular. Let’s take a look and see which batteries are best for different marine uses.

What Type of Battery is a Marine Battery?

Any discussion of the different types of marine batteries starts with the question of how the battery will be used. Other than small, pull-started outboards, all boats need a cranking battery. So whether your boat is a big, diesel-powered sport-fishing boat, a petrol-powered inboard/outboard, or a cruising sailboat with an auxiliary diesel, you need a battery to start the engine.

Apart from the engine, boats have a variety of electrical needs. Smaller boats have navigation lights, VHF radios, and often a GPS chart plotter and stereo. Larger boats need even more electrical power. Refrigeration, air conditioning, autopilots, watermakers, anchor windlasses – they all need electricity.

On smaller boats, one battery often provides all of the power. On larger boats, one or more batteries may be dedicated cranking batteries. A deep cycle battery (or more than one wired in parallel) will be used specifically to power house loads – all of the other electrical systems onboard.

Three Types of Marine Batteries

As you can see, marine batteries are called upon to do different things. That’s resulted in battery manufacturers like Thailand-based RB Battery company designing batteries specific to each purpose.

Cranking Batteries

Dedicated cranking batteries for marine use are designed to put out large amounts of power for a short period of time. Sized to match the draw of your engine’s starter, cranking batteries are optimized to deliver 75 to 400 amperes for five to fifteen seconds. Once the engine is running, the alternator quickly brings the battery back to full charge.

Dedicated cranking batteries are lead-acid batteries. They use alternating layers of negative and positive plates with insulation separating the plates. Lead-acid batteries (aka a wet cell battery) – still the most common batteries in use – have been around for 150 plus years.

More numerous and thinner plates than other batteries give extra surface. That lets cranking batteries generate brief bursts of high-amperage current. This design means that cranking batteries don’t do well discharging current over long periods. It can seriously shorten their life span. Another drawback is that the thinner plates are more fragile. That’s a disadvantage in high-impact environments.

Deep Cycle Batteries

If you think of a cranking battery as a sprinter, deep-cycle batteries are the long-distance runners in the battery world. Deep cycle batteries are designed to power all of the house loads on your boat when no other power source is available.

That cruising sailboat exploring the Great Barrier Reef? Its house bank of deep-cycle batteries is what keeps everything running when there’s no current coming from the engine’s alternator, solar panels, a wind generator, or shore power.

Unlike cranking batteries, deep cycle batteries happily tolerate being heavily discharged over relatively long periods. It’s not unusual for deep-cycle batteries to discharge up to 50 or even 70% of their capacity overnight.

Their design is optimized to put out smaller amounts of current over longer periods – the opposite of cranking batteries. That means fewer – but thicker – plates with higher antimony content. Recharging the batteries puts electrical energy back into the battery so that they are ready for use again.

Another aspect of their design is that they can repeat this discharge and recharge cycle many, many times. Sizing a house bank of deep-cycle batteries wired in parallel means some calculation is in order.

The goal is to have a house bank with enough reserve capacity to cover three or four times the amount of energy that will be used before recharging the batteries.

Dual-Purpose Batteries

The third type of marine battery are dual-purpose batteries. As the name implies, these batteries are a compromise between dedicated cranking batteries and deep-cycle storage batteries.

Dual-purpose batteries have antimony-heavy, large, thick plates and lead paste chemistry. That lets them stand up to the kinds of long discharges that quickly ruin a cranking battery. At the same time, they can discharge the amperage needed to start your engine. Because they have less capacity than a deep-cycle battery of the same size, boaters use them for specific purposes:

  • Smaller powerboats with a single battery for both starting and house loads
  • Sailboats with two batteries where either one might serve as a starting or house battery
  • Boats with a single battery bank doing double duty

Battery Chemistry

Boaters today can choose newer designs like gel or lithium-ion batteries. But, the most popular marine batteries by far are still traditional flooded, wet cell batteries or the newer AGM batteries. Why? Lead-acid batteries – AGM or flooded – offer the best performance versus cost and are proven in the tough marine environment. It’s that simple.

While flooded batteries are still widely used in marine applications, AGM batteries are increasingly popular. They are maintenance-free, affordable, and do a superb job in a dual-purpose role onboard.

That makes an AGM battery the preferred type of marine battery for more and more boaters. Other advantages of AGMs include faster charging and a very low self-discharge rate when left unattended.

The Bottom Line on Marine Batteries

What type of battery is a marine battery? It’s a battery designed and built to do a tough job under harsh conditions. For that reason, boaters need affordable, rugged, and proven batteries. Available in the three most common sizes – Groups 24, 27 and 31 – RB marine batteries are a top choice for boaters across Africa, Asia, and the Middle East.

Contact RB Battery today at their headquarters in Bangkok. They’ll be glad to offer technical support, specific battery recommendations, availability, or more information!