Can You Use Deep Cycle Batteries For Starting A Boat?

A large majority of engines or motors used in boats, whether it’s an outboard motor, an inboard motor or an inboard/outboard motor also known as sterndrive needs a battery to keep it going. A battery is used not only to start the engine but also to power all the electronic components loaded on the boat – fuel pumps injectors, electric/hydraulic power steering, and trim pumps.

A considerable amount of electricity is required to power all these, maybe, much more than what the capacity of your battery system could handle. That’s the reason why there is a need for two separate batteries to do the job; one to start or crank the engine, the starting battery, the other to deliver a steady supply of power while the boat is trolling, a deep cycle battery.

But, can you use a deep cycle battery for starting a boat? Thar question will be answered later in this article. First, let’s look at the type of marine batteries for a boat.

Types of Marine Batteries

Selecting the ideal marine battery for your boat is not just a matter of choosing the most popular brand. The ideal battery only becomes ideal or right when it is applied where it will perform best and given the correct maintenance. The selection process begins with being aware of the differences between deep cycle batteries and starting or cranking batteries, the two most accepted marine batteries.

Cranking/starting battery

The cranking/starting battery is responsible for cranking or starting the mother once the engine’s ignition is switched.on.To be able to deliver that kind of powerful energy burst the battery should have a high cold cranking amp (CCA) rating.

Cranking/starting battery has a lot more thin plates inside to enlarge the plate surface area and ensure that starting is effortless and smooth.The larger the plate surface area, the better it is for the battery to deliver the required power.

But, the very features of a starting battery that makes it fit to crank an engine are the very same features that make it unfit for cycle or continuous discharge use. This is the reason for the need for a deep cycle battery.

Deep cycle/ trolling marine battery

After the engine has started and the boat is already launched in the water, there is no longer a need for that powerful burst of energy delivered by the starting battery. What it needs is a steady and consistent supply of power for cruising and trolling in the waters coming from a deep cycle battery. That’s why a deep cycle battery is also sometimes called a trolling battery.

Trolling batteries have lesser but thicker plates. These plates give the batteries the ability to supply a continued and steady power output for a prolonged period. Deep cycle batteries are also charged and discharged repeatedly for as many times as possible. Deep cycle marine batteries are not prone to overheating. During heavy current their thick plates can endure high temperature.

Can you use one battery for both cranking and trolling? Or, Can you use a deep cycle battery for starting a boat? Let’s find out.

Any boater will be tempted to lessen the load of his boat by reducing the number of accessories it carries. Unfortunately it is quite a challenge to integrate the operation of a starting battery and a deep cycle battery.

Why? Because when a starting battery is used continuously, as in the case of trolling, it is likely to overheat and be depleted of its capacity. In the same manner that when a deep cycle battery is used for starting and compelled to provide the quick powerful burst of energy required for starting, it just might not work.

Although it can be done, use a deep cycle battery for starting a boat, it is not recommended. A two battery system is more preferred for best results.

Dual purpose marine batteries

What then is the role of a dual purpose marine battery? True, there is a dual purpose marine battery that can do the work of both a starting battery and a deep cycle battery, but unfortunately, it does not do well at both. Of course it will be one less expense and less weight on the boat but it is not recommended for all kinds of boats.

A dual purpose battery may not be able to withstand repeated and numerous charging and recharging as well as a deep cycle battery could. Many dual purpose battery could not tolerate a deep discharge. At the same time, it is prone to overheating when the condition is not so good. This could mean disaster when you are out on the open sea. But, for short trips, a dual battery will do.

Boat engine

We have been discussing about marine batteries by relying on the resource from battery man guide: battery guide and the need to have two batteries. This is under the assumption that there are also two engines- either an outboard, inboard or sterndrive motor that is usually gasoline driven and a trolling motor.

The main engine is the boat’s primary source of speed and momentum. It is switched off and the trolling motor is switched on when the boat goes on a trolling mode. The starting/cranking marine battery is used for the main motor, while the trolling battery is for the trolling engine.

A trolling motor or engine is an independent unit consisting of a propeller, an electric motor and controls. It is powered by a battery to propel the boat. It is installed either at the stern or at the bow of the boat.


So, I guess that answer your question, “can you use a deep cycle battery for starting a boat? You could, but it is not recommended. It’s true that a deep cycle marine battery can start an engine in an emergency or when necessary, but under normal condition, it is still best to have a two battery system where the engine battery is separated from the trolling battery.