Battery 101: Marine Starting, Dual Purpose and Deep Cycle Batteries

Seasoned boaters understand how crucial it is to select the right battery for their application. An under-performing battery can quickly turn a great day on the water into a frustrating experience. If you are new to boating, determining which marine battery is right for your vessel should be your first port of call before embarking on your adventure.

There are three types of batteries which can be used in marine applications. The first one is a marine starting battery which is designed for engine cranking applications. The second type is designed to support both starting and cycling applications, and is often called a dual purpose battery. Finally, there is also a deep cycle battery which is designed to specifically deliver power over extended periods. While they all can power a boat, they are designed for different purposes. In this article, we will break down the key differences between the two types and their unique features to help you to make an informed decision based on your requirements.

Overview of Marine Batteries

A key feature that sets marine batteries apart is their ability to withstand harsh vibrations. This is achieved by bonding the plate groups to each other and the battery case using hot melt glue. This added support ensures that the plates remain intact, even when exposed to the high levels of vibration and shock commonly experienced in boating environments.

Some people may opt to use a car battery in a marine application instead of a dedicated marine battery. Whilst this may work for the short term, the service life is reduced, and the warranty will be void. Car batteries are not built to handle the demanding conditions marine crafts face on the water. When used in marine applications, car batteries can suffer from plate cracking, distortion or electrolyte loss which will ultimately lead to battery failure.

What is a Marine Starting Battery?

The main purpose of a starting battery, also known as a cranking battery, is to provide short and powerful bursts of energy to start an engine. You will often see CCA (Cold Cranking Amps), MCA (Marine Cranking Amps) or CA (Cranking Amps) on the label of a marine starting battery. These 3 ratings all measure how much current a battery can supply using different standards that are recognised across the world.

Starting batteries generally have a larger number of thinner plates compared to what you would find in deep cycle batteries. The higher plate count increases plate surface area which increases the cranking power. Cranking batteries are engineered to

discharge power quickly and then be recharged by the boat’s alternator or charging system. These batteries should not be cycled, as they are not built to handle deeper discharging. As such, starting batteries are ideal for starting outboard motors, inboard engines and other marine engines.

What is a Deep Cycle Battery?

A deep cycle marine battery is designed to deliver a consistent power supply over a longer period which allows for repeated deep discharges and recharges. Deep cycle batteries have a lower number of thicker plates when compared to cranking batteries. This design improves the batteries ability to deeply discharge however it reduces its ability to deliver high bursts of power for starting an engine. Lead acid deep cycle batteries can be discharged down to 50% State of Charge (SoC), and Lithium Iron Phosphate (LiFePO4) batteries can be discharged to 95-100% SoC.

Due to these characteristics, deep cycle batteries are best suited for powering electrical systems such as trolling motors, lights, fish finders, GPS, radios and other devices which need a consistent supply of energy.

Marine Starting & Cycling Batteries

A marine starting and cycling battery (also known as a dual purpose marine battery) is a great solution for boaters requiring a battery which can start the engine as well as deliver the ability to cycle. This battery is a compromise. While they can provide quick bursts of power to start the engine, the cranking power will be less than a marine starting battery. They also have the ability to deliver power for onboard electronics and lighting however their deep cycle performance and longevity is less than a deep cycle battery. Smaller marine applications with space restrictions, or larger applications with multiple batteries can benefit from using dual purpose starting and cycling marine batteries.

Owners of SUV’s and 4WD’s will often also install starting and cycling marine batteries in their vehicles, as the added vibration resistance will increase the service life and durability in off road applications.

The Last Word

When deciding between a cranking, deep cycle or dual-purpose marine battery, there are a few things to keep in mind. Consider your power requirements, space restrictions, and overall usage. If the main battery task is starting the engine, a marine starting is the best option. If you need a battery to supply power over extended periods, a deep cycle battery is the ideal solution. If you have a smaller boat, or if there are multiple batteries in your boat which are connected in parallel, a bank of marine starting & cycling batteries may be the best and most reliable solution. In some applications, running a combination of a dedicated cranking marine battery to start the engine and a separate

deep cycle battery to support the electrical loads of the boat when the engine is not running may be more suitable.

Choosing the right marine battery is essential for your application’s performance and longevity. A seasonally used small fishing boat doesn’t need a starting battery and a deep cycle battery to slow it down. A dual purpose marine battery is perfectly suitable for this situation. Similarly, using a cranking battery to power a range of onboard electronics will damage the battery quickly as it is not designed to cycle; a deep cycle battery is a much better option in this case.