What to Know About Marine Batteries

As you shop for batteries for your solar installation, there’s a good chance you may come across marine batteries and wonder if they are a viable option for your system. Especially if you’re looking to add solar to your boat, a marine battery may seem like the best option. But that isn’t always true. What’s potentially confusing about this shopping process is that marine batteries can be a variety of different battery types, from starter to deep cycle. Not all are suitable for a solar installation. Let’s discuss so you know what to look for when deciding on a battery solution.



What are deep cycle batteries?

Deep cycle batteries look similar to car batteries, but they are actually very different. Deep cycle batteries are what you’ll need for your solar installation, since contrary to a car, you’ll need power for a long period of time and not just in a short burst.

In contrast to car batteries which only provide short bursts of energy, deep cycle batteries are designed to provide sustained periods over a longer period of time. Deep cycle batteries can, in theory, be discharged up to 80%, but most manufacturers recommend not discharging below 45%. Regularly going beyond that point will shorten the life of the battery.



How do solar batteries work?

Solar batteries store the energy that is collected from your solar panels. The higher your battery’s capacity, the more solar energy it can store. In order to use batteries as part of your solar installation, you need the following components: solar panels, a charge controller, and an inverter.

Your solar panels will first need to be connected to a charge controller which will help monitor how much energy is stored in the batteries to prevent overcharging. Charge controllers will also shut down a system if the batteries become too depleted. Before powering your appliances, your batteries will need to be connected to an inverter to convert the DC energy collected from solar panels and converted to AC energy.

When using batteries for solar panels as part of a home solar system, you’re able to store the excess electricity your panels produce instead of sending that energy back into the grid. Electricity will be sent to the grid if your batteries are fully charged and your panels are still producing energy.



What are marine batteries?

Marine batteries can either be starting, dual-purpose, or deep cycle batteries. They are often a hybrid of starting and deep cycle batteries, known as dual purpose. They have lead sponge plates that are heavier than starting battery plates, but not as thick as deep cycle battery plates. It can be difficult to tell what you get in a marine battery, and the words "marine" and "deep cycle" are often used interchangeably. They are often used in marine applications due to their small size that makes them suitable for boats.



What’s the difference between starting, dual purpose and deep cycle batteries?

Starting Batteries: Starting batteries are designed to discharge a big burst of energy for a short period of time. This makes them ideal for automotive engines. One of the key differences between a starting battery and a deep cycle product is the thickness and number of charged plates. Starting batteries rely on a greater number of thinner plates to push the high energy burst to start an energy.

Dual Purpose: Dual purpose batteries land in between starting and deep cycle batteries, as the name suggests. The intention behind them is to create improved performance and lifespan. The energy storage of dual purpose batteries are lower than deep cycle counterparts, but higher than starting batteries. Many people opt for dual purpose batteries to serve as both your cranking battery and to also power your trolling motor.

Deep Cycle: Deep cycle batteries are designed to discharge a small amount of energy over a longer period of time. Think of them as the marathon runner of batteries that work great at powering appliances in your home. Marine deep cycle batteries are available in various flooded, sealed lead acid (AGM or gel), and lithium iron phosphate options. Each of these types offer different benefits around efficiency and maintenance levels.



How long do marine batteries work?

Battery life varies a bit from technology to technology. For example, many gel batteries typically last 1,100 cycles, absorbed glass batteries 600 cycles, and lithium iron phosphate batteries 7,000 cycles. It’s fair to assume the general range for a solar battery’s lifespan is between 5 and 15 years. An AGM (absorbed glass mat) deep cycle battery usually lasts for four to eight years, a gelled deep cycle battery for two to five years, and an industrial deep cycle battery for 10 to 20 years.

The lifespan of a deep cycle battery depends on how and where it is used and maintained. While the variables make it difficult to provide a definite life span, typically a marine battery lasts for one to six years.



Should I use a marine battery for my system?

If a marine battery is a deep cycle battery, this will work for your solar installation. However, don’t let the ‘marine’ label overpower everything else, especially if you are looking for solar for a boat or marine application. Any of Renogy’s deep cycle batteries will all work great on a boat. We even have a variety of kits available that take into account marine spatial requirements.



How many batteries will I need?

The amount of battery storage you need is based on your energy usage. Energy usage is measured in kilowatt hours. For example, if you need 1,000 watts for 8 hours per day, then your energy usage is 8kWh per day. A battery capacity of 4 to 8 kWh is usually sufficient for an average four-person home.

To size a system that will best fit your needs, we recommend making a list of all the devices you plan on running. Get the wattage information, or the amps and volts of the product, and provide an average run time per device. The Renogy solar panel calculator is a great tool that makes it a quick and easy process to help determine your specific needs.



Conclusion

If you’re looking to add solar to your boat, it’s important to purchase the right battery for your system. While you may be tempted to just purchase a marine battery and assume you’re safe, many marine batteries, in reality, aren’t suitable for solar installations. What you will want to look for is making sure the marine battery is a deep cycle battery that will be able to provide your solar installation with energy over longer periods of time. When in doubt, check out Renogy’s deep cycle batteries or marine kits.