What to Know About Deep Cycle Batteries for Solar Storage

What to consider when selecting a solar storage solution

So you’re excited about solar and have finally selected your solar panel kit. If you’re in an RV or van, you’ll need a way to store that energy produced from your panels. If you’re going solar at home, maybe you’re interested in going off-grid and utilizing battery storage. There’s a lot to take into consideration when deciding on a solar storage solution. Let’s break it down for you.

What are deep cycle batteries?

Deep cycle batteries look similar to car batteries, but are actually very different. In contrast to car batteries which only provide short bursts of energy, deep cycle batteries are designed to provide sustained period over a longer period of time. Deep cycle batteries can 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 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 becomes too depleted. Before being power 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.

Do I need battery storage?

I live in an RV, camper, or motorhome: Yes!
We highly recommend battery storage in your RV. This way, your solar panels and batteries can take the place of a gas-powered generator. You’ll be able to keep things running even when your panels aren’t producing energy.

I live in a home with access to the electrical grid: Not a requirement, but is useful in case of outages.
Battery storage can be beneficial for homeowners, but it is not a requirement. If you’d like to go off-grid or be able to run your solar panels in the case of grid outages, battery storage is a great way to to ensure continued energy access.

What are the different types of batteries?

There’s a range of deep cycle battery options.The most common ones used for solar installations are flooded lead acid, sealed lead acid, and lithium iron batteries. Flooded lead acid batteries are the most inexpensive option and are available at most big-box and auto stores. Sealed lead acid batteries store 10 to 15 percent more energy than lead acid batteries and charge up to four times faster. Lithium iron batteries are the most expensive options, but also last four times longer than lead-acid batteries and weigh much less.

What should I consider when deciding on a deep cycle battery for my solar panels?

When shopping for deep cycle batteries for your solar installation, there’s some different factors to consider: price, capacity, voltage, and cycle life.

Price: Batteries can vary from around $100 for the cheapest lead acid battery to more than $1,500 for a lithium iron battery. Be sure to consider the ultimate lifetime and not just upfront costs, as you will have to replace lead acid batteries before you will need to replace a lithium iron battery. You’ll also need to do more maintenance on a flooded lead acid battery, and we all know time means money.

Capacity: Battery capacity is important because it measures the amount of energy you can store. If you need to power certain appliances for long periods of time, you'll need more batteries to carry a bigger load. Capacity is measured in total amp hours.

Voltage: Be sure to check the voltage of the battery bank to ensure it is compatible with your panels and the rest of the system, particularly your solar panels. Panels typically come in either 12V and 24V options. Most RV’s and boats typically use 12V battery banks, so people usually stick with the 12V panels. The advantage of using a higher voltage battery bank is that is saves you money in the long run as you need less charge controllers and can use thinner cables for the same amount of power. If your energy needs are over 3KW, go for 48 volt system. Large off-grid houses often use 48V.

Cycle Life: This specifies the number of discharge and charge cycles a battery can provide before the capacity drops below the rated capacity. This varies sharply from technology to technology and is measured in number of cycles.

Which deep cycle battery is best for me?

Flooded Lead Acid: Cheap, but high maintenance
Cost: Around $100

Flooded lead acid batteries are the cheapest, but also require the most maintenance. You have to check water levels with a hydrometer and add water to keep them topped off each month. Lead batteries must be housed in a ventilated room since they emit gases. This is not necessary with lithium-ion batteries.

Sealed Lead Acid (Absorbed Glass Matt and Gel): Little maintenance, lower charge rates
Cost: $239-$449
Shop on Renogy for Gel and AGM Batteries

Contrary to flooded lead acid batteries, sealed lead acid batteries require little to no maintenance and are spill-proof. They are more expensive than flooded lead acid batteries, but also have a much longer cycle life. Within the family of sealed lead acid batteries are two types: absorbent glass matt (AGM) and gel batteries.

Gel batteries, which use silica to stiffen the electrolyte solution in the battery, tend to have lower charger rates and output than absorbed glass matt batteries. They also can’t handle as much current, meaning they take longer to recharge. However, gel batteries have a greater lifespan than AGM batteries and can be mounted in any orientation. Absorbed glass matt batteries offer a better temperature range and are a bit cheaper than gel batteries.

Lithium Iron Phosphate: Expensive, but zero maintenance and long lifespan
Cost: $499-$1499
Shop on Renogy

Lithium iron phosphate batteries are the most expensive battery option, but they have an extremely long cycle life, high discharge and recharge rates, and are incredibly compact and lightweight. They also require little to no maintenance.

Lithium batteries typically have a lifespan of at least 10 years. Lithium iron phosphate batteries also lose less capacity when idle. This is especially useful in cases where solar energy is only used occasionally. They also have the best cycle life of deep cycle batteries, offering approximately 2000 cycles at 100% DoD (depth of discharge.)

Do lithium batteries charge faster than flooded lead acid batteries?

Yes! As mentioned above, lithium iron phosphate batteries are more efficient and have a faster rate of charge. This is because they can typically handle a higher amperage, which means they can be recharged much faster than sealed and flooded lead acid batteries. Lead acid batteries are limited in how much charge current they can handle, mainly because they will overheat if you charge them too quickly.

How many deep cycle 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.

Can I wire different deep cycle battery types and sizes together?

We recommend wiring batteries of the same type and amp hour rating, i.e. if you go with absorbed glass matt batteries, all the batteries in your battery bank should be AGM batteries. This will limit any efficiency loss due to having different batteries.

Are solar batteries safe?

Yes! In general, solar batteries are very safe. Issues that may arise come if they are installed incorrectly or the battery quality is low. Because of that, it is important to ensure batteries are properly installed and are purchased from a reputable manufacturer.

Lithium iron phosphate batteries have a slightly higher risk of overheating than others if installed incorrectly or supplied from an unreliable manufacturer. However, in most cases lithium iron batteries rarely pose a risk to homeowners. Renogy deep cycle solar batteries have a BMS, which stands for Battery Management System. The BMS safely protects the battery from being used/charged during incorrect conditions.

How long will it take to charge a deep cycle battery?

Total charging time depends on the weather, as well as state and type of battery. If a battery is completely drained, a panel can typically charge the battery within five to eight hours.

The total charging time will vary depending on the state of a battery. If a battery is totally drained, a solar panel can energize the cells within five to eight hours. The position of the sun in the sky can impact a panel’s charging speed. When sunlight shines directly on a panel in the middle of summer, the charging speed will be faster. Charging cycles are slower on cloudy days.

What is the lifespan of deep cycle batteries?

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. Therefore, you may need to replace your batteries at least once within the lifespan of the rest of your solar system.

Although many people focus on the performance of solar panels when planning a solar installation, one cannot afford to forget to take the time to weigh the different battery options available to you. After all, a poor functioning or under performing battery can reduce the overall solar system performance and end up costing you thousands in the long run.


Deciding on the right solar storage solution can be challenging with all of the deep cycle battery options available. Flooded lead acid, sealed lead acid, and lithium iron phosphate all have their own advantages, from maintenance levels, to cycle lives, and charge rates. There’s not a one-sized-fits-all solution, but by weighing those costs and benefits you’ll be able to build a battery bank that works best for you.