Deep Cycle Vs. Dual Purpose Vs. Starting/Cranking Battery For Trolling Motors

Choosing your battery and charger systems wisely may save you a lot of time and money in the future.

Batteries are the lifeblood of trolling motors on modern boats. Besides just performing the basic function of starting up its motor, batteries are responsible for running many different features such as navigation lights, fish finders, aerator pumps, stereos, and any other electronic accessories you may have on board.

However, picking new batteries for your boat can be an overwhelming task since each boat has unique characteristics and power requirements depending on its electrical features, engine capacity and construction.

Before you all-out make a purchase, it is crucial for you to evaluate the advantages and disadvantages of all three options of batteries to decide which will be the best choice for your trolling motor and its unique power needs.

If you keep scrolling through, we will review three types of batteries for trolling motors, their applications, and their specific advantages and disadvantages. Let’s first start with a short overview of each battery:

1. Deep Cycle Batteries

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The trolling motor of a boat depends on these batteries. Deep cycle batteries can be described as the marathon runners of your boat’s trolling motor since they are responsible for powering its electrical loads when no alternative charging source is available (whether solar panel, wind generator, engine alternator, or shore power charger).

Deep cycle batteries are designed to discharge energy over a longer period of time, since they use about 50% to 80% of their battery capacity and also have the ability to recover fully afterwards.

Deep cycle batteries tend to have thicker plates as compared to starting batteries and, therefore, tend to be a lot heavier than starting batteries with similar dimensions.

2. Dual Purpose Batteries

To put it simply, dual-purpose batteries have the ability to function as both deep cycle batteries and starting batteries. With thicker and larger plates as compared to starting batteries, these batteries are known to be the best option for handling deep discharges, which typically ruin most starting batteries.
This particular class of battery is made up of some liquid, which is just enough to hydrate internal plates so that nothing leaks or breaks out. In addition, these batteries are designed to be stable, durable, and have the ability to start the boat’s engine while also powering all of its electrical components for an entire day out in the water.

3. Starting Batteries

Also referred to as cranking batteries, starting batteries are commonly known to power a boat’s starter motor, enabling its engine to start, but that’s not all. These batteries can get depleted easily and they rely on the engine’s alternator for recharging.

Starting batteries house positively and negatively charged plates, which are divided by insulation. The main difference between these batteries and deep cycle batteries is their thickness and the amount of charged plates.

Other than engine starts, these batteries are also commonly used to power bilge pumps, courtesy lights, navigation systems, aerators, and other general electronics on a boat.

Deep Cycle vs. Starter Batteries

Most people tend to be familiar with those large car batteries, but in reality, there are only two types of batteries that need to be considered for trolling motors: starter batteries or deep cycle batteries.

Typically, starter batteries are meant to crank a boat’s engine with a momentary burst of power, whereas a deep-cycle battery is designed to keep providing a continuous flow of power. Even though both of these batteries may seem quite similar from the outside, they have quite a few differences when it comes to design.

While starter batteries are designed to provide higher peak powers and no deep cycling, deep cycle batteries produce moderate levels of power output with effective cycling. That said, it’s time to dig a little deeper and have a look at the technical differences between the two batteries.

Starter batteries come with a CCA (Cold Cranking Amp) rating, which is imprinted in terms of amperes. This rating signifies the amount of current this battery will be able to deliver in cold temperatures. The Society of Automotive Engineers (SAE) specifies that the battery should produce 30-seconds of discharge at 18 degrees Celsius (0 degrees Fahrenheit) at its rated CCA ampere without falling below 7.2 volts.

Starter batteries also tend to have a pretty low internal resistance, which is achieved by manufacturers by adding an additional number of plates to provide for more surface area. The plates in these batteries are thin. Lead is applied here in what appears to be a fine foam and looks like a sponge.

If you could see inside a starter battery, you will see a number of thin plates lined up in parallel so the battery can achieve a low resistance with more surface area. This arrangement manages to extend the overall surface area of the plates so that it can achieve maximum power and low resistance. Of course, this also means that starter batteries add more emphasis on power as opposed to capacity. Also, the thickness of plates is also less important since the discharge tends to be short and the battery gets recharged during the drive.

Deep cycle batteries for trolling motors are manufactured for high cycle count and maximum capacity. The manufacturers of these batteries achieve this by making the plates in the battery thick. Even though these batteries are designed for deep cycling, a full discharge still produces stress, and the number of cycles depends on its depth-of-discharge (DoD). You will also find that deep-cycle batteries commonly marked in minutes of runtime or Ah.

Our Verdict

Starting batteries allow your boat to start by powering the engine when its ignition switch gets activated. This is the reason why they are known as ‘starter batteries’. Once the engine has been started, the boat no longer requires those powerful and quick bursts of high energy produced by starter batteries. Simply put, the same elements that make this battery perfect for cranking your boat’s engine, also make it less ideal for cyclic use or continuous discharge.

This is why deep cycle batteries are also known as trolling batteries. They can be recharged and drained multiple times, which is a trait starting batteries lack.

•     Starting batteries make sure the boat can start easily and make its way into the water.
•     Deep-cycle batteries keep the boat operational while running its electronics in every possible condition.

Why Can’t We Use the Same Battery for Trolling and Cranking?

We understand it can be really tempting for boat owners to want to try and minimize their accessories and additional components in their vessel.

However, this approach will only end up costing you more time and money in the long run. It is very difficult to try and combine the unique benefits of starting batteries and deep-cycles batteries into just one battery, since both of these batteries have been specifically designed to perform different jobs.

When starting batteries are put through continuous use (which is bound to be the case for trolling), it will overheat and deplete its available capacity.

Similarly, when deep-cycle batteries are made to provide short bursts of energy that is necessary for starting up an engine, it wouldn’t always be able to perform.

There Is a Third Option: Dual Purpose Batteries

Where there are rules, there are exceptions.

Dual-purpose batteries are designed to work for both trolling and cranking. However, this feature doesn’t necessarily make them the perfect choice for all boats. Even though dual-purpose batteries do technically mean that you will invest in and maintain just one battery, they don’t necessarily allow the boat to perform as effectively as 2 batteries will.

For example, deep-cycle batteries are tailored to withstand multiple recharges and discharges where starting batteries aren’t. Therefore, dual-purpose batteries tend to fall somewhere in the middle.

Many dual-purpose batteries do not work too well with total discharges (i.e. discharges that are over 50% of their usable capacity. Dual-purpose batteries also tend to be more prone to getting overheated in harsh environments, which is certainly not good news when you’re out at sea. Still, this hybrid form of battery tends to work pretty well for short trips or if they are being maintained in the right manner.

Dual Purpose vs. Deep Cycle Batteries

As you probably already know, trolling motors and other similar accessories tend to deplete power at a much slower rate and for longer periods at a time. The batteries that power these marine accessories are commonly not recharged until the very end of your day out at sea.

Since deep-cycle batteries are so prone to deep discharges, they tend to be very hard on their battery plates. For this reason, they are designed with thicker, yet fewer lead plates as opposed to cranking batteries that have been built to cater to deep cycling.

Deep cycle batteries have a reserve capacity rating (RC) which is meant to indicate how long it could carry specific loads before it is rendered into the dead zone. The higher the battery’s RC number is, the longer this battery will be able to power your boat’s accessories.

Always remember this when you’re choosing your battery. Ideally, deep-cycle batteries tend to have 2- or 3-times more RC than starting batteries. Deep-cycle batteries can also withstand close to a hundred recharge and discharge cycles whereas we’ve already concluded that starting batteries aren’t designed for total discharge.

Our Verdict

Considering all of the above, it is usually considered wise to install both deep-cycle and starting batteries separately. However, if you drive a smaller boat, you might be dealing with limited storage space and weight restrictions.

If this is the case, you should consider investing in dual-purpose batteries that are specifically manufactured for both, cycling and starting. However, do bear in mind that most dual-purpose batteries don’t have the ability to start a boat’s engine as efficiently as a good starting battery. Speaking of which, it wouldn’t be able to endure the number of deep discharge or recharge cycles as compared to deep-cycle batteries.

Which Should You Choose?

For light-to-moderate amp draw service, we recommend that you choose a dual purpose battery specially designed to deliver both starting and cycling.

If you’re dealing with heavy-duty cycling, then you will be better off with a deep-cycle battery. This battery will provide you with enough starting power and cranking amperage to get your engine running as well as enough reserve power to have your trolling motor and other electronic accessories running for a longer period of time.

Use the following chart to determine which kind of battery is appropriate for your particular situation:

Consider Your Power Usage

Conclusion

Starting batteries have the ability to deliver large bursts of power for short periods of time as is typically the case with engine startups. Unlike deep-cycle batteries, these batteries aren’t designed to be able to withstand numerous discharge and recharge cycles, and draining them may shorten their lifespan significantly.

Deep-cycle batteries offer users the opportunity to discharge and recharge as many times as possible without the risk of damaging or shortening its lifespan. For this reason, they are better suited to power numerous plug-in and electronic devices, as well as having a high demand for trolling motors. However, to make an informed decision, do make sure to check the deep-cycle battery’s CCA rating in order to make sure it has enough power for your boat.

Finally, dual purpose batteries are a good choice for your boat if you have limited storage space or are dealing with weight restrictions. Don’t forget, however, that dual purpose batteries wouldn’t deliver as good of a result in either function as starting or deep-cycle batteries.

If you’re considering buying a car battery instead of a deep-cycle battery, click here to have all your questions answered and to find out why they cannot be used interchangeably.