The best solar batteries allow you to store the energy you produce from your solar panels and use this energy to power your gadgets and appliances whenever you need it.

Solar batteries allow you to use solar energy when you need it rather than be limited to its use when the sun is shining. It also maximizes your return on investment for your solar panels, as electricity used for your personal needs is more valuable than selling your excess production to your electricity grid.

The best solar battery on the market differs for every user. Some solar system owners will prefer a system with a large capacity that can power their needs for a longer period. Other owners will need a solar battery that can produce larger amounts of electricity over a shorter period, such as during an interruption of electricity provided by the local grid.

It would be best to consider important battery capacity, energy rating, depth of discharge, and round-trip efficiency when choosing what battery works best for your needs.

Best Solar Batteries in 2021 at a Glance

  1. Mighty Max Battery 12VBest for Emergency Use
  2. NPP NPD 12Best for Marine and RV Camping
  3. Discover AES LiFePO4 Deep Cycle BatteryBest for Large-Scale Solar Systems
  4. LG RESU BatteryBest for Upgrading Systems
  5. Tesla Powerwall 2Best for Everyday Use

Our List of the Best Solar Batteries Reviewed

1. Mighty Max Battery 12V

Mighty Max Battery 12VThe Mighty Max Battery 12V is a lead-acid rechargeable solar battery that provides amazing storage for solar energy. It is a very versatile solar battery that can provide exceptional performance in both low and high temperatures. This solar battery improves the design of typical lead-acid batteries by incorporating absorbed glass mat (AGM) technology.

The maximization of the electrolyte over the surface of the plate provides the superior performance of these batteries compared to traditional lead-acid batteries, such as the NPP NPD 12 reviewed in this article.

Safety

The Mighty Max Battery 12V provides improved safety for homeowners. This battery boasts a safety feature that helps if the battery gets overcharged. When this happens, one-way valves allow the excess oxygen and hydrogen that are produced to escape. This ensures that gases do not build up and that users are kept safe from potential fire hazards. This makes the Mighty Max Battery 12V a safer solar battery option than others on this list, including the LG RESU series and the Telsa Powerwall 2.

Slow Discharge Rate

Its slow discharge rate allows you longer use before having to recharge it again. However, when using the Mighty Max Battery 12V to power bigger appliances, it can discharge much faster than using it for smaller devices.

Ease of Installation and Use

There is no need to add distilled water or provide any other regular maintenance for this battery. It can be mounted in just about any position and function without leaking electrolyte within the battery.

The one caveat here is that its outer casing can at times not be as sturdy as with other batteries like the NPP NPD 12, so it should be handled more carefully. But it is one of the best batteries in terms of ease of maintenance and installation.

Pros

  • It has a long battery life
  • Features a slow discharge rate
  • It can be used in high or low temperatures
  • Features a safety valve that prevents gas and pressure buildup
  • Provides high energy surge to power electronic devices

Cons

  • The battery’s cycle is shorter in frigid temperatures
  • Battery discharges quicker if used to power larger appliances
  • The casing needs to be handled somewhat carefully
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2. NPP NPD 12

NPP NPD 12

NPP was founded in 2002 and specialized in R&D as well as the manufacture and sale of sealed lead-acid batteries. The NPP NPD 12 is a lead-acid battery with a deep cycle that can power various systems. It is one of the best deep cycle batteries for solar storage.

Versatility

This versatility allows the NPP NPD 12 to be one of the best solar batteries for powering alarm systems, emergency lighting, computer or telecommunication systems, fire prevention equipment, or to serve as a standby power system. This multitude of effective uses is an extremely nice feature of the NPP NPD 12, similar in its versatility to the Tesla Powerwall 2.

Depth of Discharge

These deep-cycle batteries are rechargeable. In other words, you can fully utilize its capacity to provide you the energy you need. However, discharging the battery regularly shortens its life. For example, this battery can produce about 350 cycles with 100% DoD. But at a DoD of 30%, your battery can last for approximately 1500 cycles. So do not drain your battery often to extend its life.

Durability

The casing of this battery features non-conductive ABS plastic. This makes the NPP NPD 12 particularly resistant to vibrations, harsh weather, chemicals, and shocks. As a result, it is safe to use this battery inside your home and is more durable than other lead-acid batteries like the Mighty Max Battery 12V or the Discover AES LiFePO4 Deep Cycle Battery.

Pros

  • Allows you to maximize its capacity in providing you energy
  • Features a long lifespan
  • The casing is very durable
  • Provides energy for a long time before discharging

Cons

  • Its longevity greatly impacted at temperatures greater than 77° F compared to other solar batteries, including the Mighty Max Battery 12V.
  • Potential issues with disposing and recycling
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3. Discover Deep Cycle Battery With Lithium Iron Phosphate LFP

Discover AES LiFePO4The Discover AES LiFePO4 Deep Cycle Battery is great for solar system uses that require deep cycling daily, such as peak load-shaving, off-grid applications, and self-consumption. It features a lithium iron phosphate LFP, a better lithium battery for stability, safety, and providing a large electrical surge to power electrical appliances.

Discover AES batteries feature a built-in BMS (battery management system) that allows cells to charge quicker and extend their lives. If specified parameters are not met for longer than two minutes, the battery shuts down to protect its integrity. The BMS monitors battery voltage, battery temperature, cell module voltage, battery current, and its state of charge to ensure that it works properly and lasts a long time.

Battery Capacity

Each Discover AES LiFePO4 Deep Cycle Battery features 6.6 kWh of solar storage, which is less than the 13.5 kWh of the Powerwall 2 and about as much as the lowest capacity battery of the LG RESU series. However, up to ten batteries can be used parallel to provide you with 66 kWh of solar storage.

And note that this battery provides greater than 90% of its original energy storage system for ten times longer than a lead-acid battery.

Charge Efficiency

The BMS enables the Discover batteries to connect for higher output and faster charging than other solar batteries. The charge efficiency of the Discover AES LiFePO4 Deep Cycle Battery exceeds 95%, which results in reduced energy bills and reduced charge times. For a point of comparison, flooded batteries typically feature a charge efficiency of 85%.

Easy Installation

This battery features very straightforward installation and maintenance. There are no cabling components for connecting batteries, as you can connect batteries in parallel without using a busbar. And given the larger size of the Discovery battery, you will need to connect fewer batteries to serve your needs. Also, note that there is no maintenance required for these batteries.

Pros

  • BMS enables efficient charging and monitoring of your battery
  • Stackable up to 10 batteries for a total capacity of 66 kWh of solar storage
  • Charge efficiency of 95% and higher gives you a better ROI and efficiency
  • LFP provides enhanced stability and safety
  • Relatively painless to install and requires no maintenance

Cons

  • Not suitable for outdoor use
  • Cost per kilowatt-hour of capacity can be slightly more expensive compared to competitors.
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4. LG RESU Battery

LG RESU Solar Batteries

LG Energy Solutions, formally known as LG Chem, produces a wide range of stationary lithium-ion batteries. Their RESU (home energy storage system) products include 48 V and higher 400 V battery options. The LG RESU series comes in 6.5 kWh, 9.8 kWh, and 13 kWh options, and this flexibility in capacity makes it one of the best batteries for solar storage.

Capacity

The usable capacity of LG RESU batteries is 90% for all 48V options. Also, note that two 9.8 kWh batteries can be linked to creating a 19.6 kWh battery capacity to accommodate the needs of a larger residential system. This provides a larger capacity than other battery options like the Discover AES LiFePO4 Deep Cycle Battery of 6.6 kWh.

Installation

LG RESU solar batteries all feature an IP55 rating, which means that they are suitable for installation in a location that is semi-outdoors. However, LG RESU batteries should not be positioned in direct sunlight. This is particularly important during the summer months.

Lifespan

LG RESU batteries can be discharged to almost full capacity every day while maintaining their performance for a long time. More specifically, LG RESU batteries can discharge and charge every day over ten years while retaining 60% or more of their capacity.

Efficiency

Another advantage of LG RESU solar batteries is their production process. This results in batteries that are more efficient, compact, and lighter than most competitors.

Another efficiency advantage is that LG RESU batteries are DC-coupled. This allows them to charge from solar panels directly instead of converting to AC first before charging the battery, as is required with the Tesla Powerwall 2. This system is much more energy-efficient and is one of the reasons it is among the best batteries for solar storage.

Warranty

LG RESU batteries come with the promise that they will retain 60% or more of their initial storage capacity for either ten years or until the battery produces 22.4 MWh (megawatt-hours) of total electricity, whichever comes first.

Pros

  • Can link two batteries to form 19.6 kWh solar energy storage
  • Lighter weight and more compact size compared to competitors
  • Depth of discharge of up to 95% of battery capacity
  • Long lifespan of 10 years or more
  • Different battery options are available depending on your needs

Cons

  • Warranty doesn’t include explicit protections from materials and equipment defects.
  • Prolonged exposure to excessive heat greatly compromises its performance
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5. Tesla Powerwall 2

Tesla Powerwall Solar Batteries 2

Tesla Energy is a major player in energy storage as well as producing quality solar panels. Its initial foray into solar battery storage made a huge impact with the introduction of its first Powerwall. The Powerwall 2 was introduced in 2016 with many upgrades over their original solar battery storage, including increased solar storage capacity and an integrated battery inverter/charger.

Capacity

The Powerwall 2 features a usable capacity of 13.5 kWh, the biggest storage option among the batteries on our list and the market today. It also has a 100% DoD.

For larger energy needs, the Powerwall 2 can feature up to 9 batteries linked in series.

This makes the Tesla Powerwall 2 a much better option than LG RESU for larger capacity systems.

Power Rating

The power rating of the Powerwall 2 is quite high at the peak of 7 kW and continuous output of 5 kW. This amount can meet the typical requirement of an average home that features a few high-powered devices or appliances running simultaneously. Note that the peak output can only be maintained for ten seconds, making it appropriate for brief power surges but not for many off-grid applications.

Versatility

The Powerwall 2 is the only solar battery on the market to utilize a liquid thermal management system that provides many important benefits. For example, it allows the battery system to function across a wide temperature range of 4° F up to 122° F. Note that, like all lithium batteries, its power output will likely be compromised at temperatures above 104° F.

Another amazing feature of this system is that it allows the solar battery to charge at temperatures below freezing. This is a significant advantage over other batteries like the Mighty Max Battery 12V that suffer from greatly reduced recharge rates at low temperatures.

The cooling system of the Powerwall 2 enables it to expel greater heat compared to other solar batteries. This results in a longer lifespan and increased performance at higher temperatures compared to its competitors. This factor sets it apart as one of the best batteries for solar energy storage.

Pros

  • The largest capacity of any solar battery on the market
  • 100% depth of discharge
  • Great warranty of 10 years of 70% capacity retention
  • The ability to ground mount makes storage more convenient

Cons

  • The size of the battery is quite large and weighs around 120 kg.
  • Not well suited for off-grid applications.
  • Relatively high conversion losses result in approximately 90% round-trip efficiency.
  • Tesla planning on forcing customers to bundle its solar panels with the Powerwall
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A Buyer’s Guide for the Best Solar Batteries

Types of Solar Batteries

A residential solar system predominantly uses one of four types of solar batteries- lead-acid batteries, lithium-ion batteries, flow batteries, or nickel-based batteries.

Lead-acid Batteries

Lead-acid batteries have been used for energy storage since the 1800s. And despite incredible technological advances in many areas of society, these batteries are commonly used with solar panels due to their amazing reliability. They remain among the best solar batteries on the market today.

AGM is a manufacturing process used in producing sealed lead-acid batteries. During this process, microscopic glass fibers are intertwined to create a glass mat separator. This separator is positioned between every lead plate in your battery. This glass separator allows for an even distribution of the electrolyte throughout the surface area of the surrounding lead plate(s) due to its incredible ability to hold onto acid.

This type of solar battery is not only reliable but is also one of the most cost-effective options for energy storage. A bonus is that recycling or disposing of these batteries is relatively straightforward because they have been around for many years.

There are two common types of these batteries used for storing solar energy, a flooded and a sealed lead-acid battery.

Flooded Lead-acid Battery

Flooded lead-acid batteries are among the most common solar batteries used for an off-grid solar panel system. It is relatively affordable and easy to dispose of when needed.

To install these batteries, you must provide adequate ventilation since they emit gases. Furthermore, these batteries require frequent maintenance since every cell in the battery must flood with water before conducting electricity (hence the name “flooded” lead-acid battery). Adding water to the battery every couple of months helps keep the cells submerged.

Another limitation with a flooded lead-acid battery is that it cannot install on its side due to its ability to leak potentially harmful compounds into the surrounding area.

Sealed Lead-acid Battery

A sealed lead-acid battery does not require the same degree of hands-on maintenance compared to a flooded lead-acid battery. Additionally, this type of lead-acid battery is self-contain, posing no risk of spills. There is no need to add water, and this battery type is better at retaining its charge than a flooded lead-acid battery.

Lithium-ion Batteries

As electric vehicle use has become more and more common, technological developments have also benefitted solar battery systems. Solar companies have tapped into lithium batteries for solar storage. Today, lithium-ion batteries are among the best solar batteries used for residential solar panels.

These lithium batteries are deficient maintenance and feature a higher battery energy density compared to lead-acid batteries. This is a critical factor for many solar systems as it saves valuable space for the location of the battery. These solar batteries also have a longer life span and often have longer warranty periods.

The main downside of lithium-ion batteries is their cost, as they are often much more expensive than other solar batteries.

Nickel-cadmium Batteries

Nickel-cadmium (Ni-Cd) batteries have been around since the late 1800s. But it wasn’t until the 1980s when they were redesigning them, that they could store the large amount of energy required for solar panels. Even still, this type of battery is not as commonly used as other types of solar batteries. This is not small because cadmium is very toxic, and some countries have even banned the use of cadmium as a result.

Flow Batteries

Flow batteries are a promising technology in the energy storage field. In this type of battery, a water-based electrolyte liquid flows between two separate tanks or chambers inside the battery. During charging, chemical reactions enable storing energy to release.

One of the biggest advantages of this type of solar battery is that it can use all the energy stored in your solar system without causing damage to the battery. In other words, flow batteries have a 100% depth of discharge. They are also deficient maintenance and can last for 30 years.

The problems with flow batteries currently include their high price. They also must be huge due to their current low storage capacity and low discharge and charge rates.

Comparing Solar Batteries

When deciding the best solar batteries for your solar panels and solar panel system, you need to consider important factors such as battery capacity, power rating, depth of discharge, round-trip efficiency, and warranty.

Battery Capacity

Battery capacity is simply the total electricity amount that you can store using your solar batteries. Solar batteries work in kilowatt-hours (kWh).

So how many solar batteries do you need? The average household in the U.S. consumes about 30 kWh per day, while the average solar battery can store 10 kWh.

But most solar batteries are usually stackable, enabling you to combine multiple batteries in your system when necessary for your solar panel system.

Power Rating

It is also important to consider the power rating of your solar battery. Power rating represents how much electricity a battery can give off at any given moment. It measures in kilowatts (kW).

So how does battery capacity relate to power rating? Well, if your solar battery has a low power rating but a high capacity, it could provide you with a small amount of electricity over a long period of time. This may be perfect if you want to power a few small appliances for a long time. But if you need to power many appliances, you may prefer a high-power solar battery with a lower capacity.

Depth of Discharge

Depth of discharge (DoD) refers to how much charge your battery needs to maintain. The chemical composition of your battery determines this. A higher DoD translates to you being able to use more of your battery’s capacity. It would help if you targeted a battery with a DoD of at least 40%.

Round-trip Efficiency

An energy measure of how much power you get from your battery depends on how much energy your battery consumes as it charges. Similar to the DoD, a higher number in a battery’s round-trip efficiency is generally more cost-efficient for you. Aim for around 80% round-trip efficiency for your solar battery.

Warranty

Solar batteries work for a long time. But all batteries feature declining performance over time. So it is important to consider the warranty of your solar batteries. This helps eliminate any risk of your solar battery underperforming.

Wrapping Up

The best batteries for solar applications feature the right combination of capacity and power rating to serve your needs. Having the right storage size and the power to run your devices and appliances is the number one priority for any solar system.

It is important to factor in your solar batteries’ discharge depth and round-trip efficiency upon determining these conditions. These qualities are critical in determining critical system characteristics, such as the amount of storage space required for your solar batteries and your return on investment for your solar system.

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