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Solar Panel Store Blog — Batteries

Which type of battery is best for solar applications?

Which type of battery is best for solar applications?

There are several types of batteries that can be used for solar power systems, but the best type of battery will depend on your specific needs and circumstances. Some common options include lead-acid batteries, lithium-ion batteries, and nickel-metal hydride batteries. Each of these types of batteries has its own advantages and disadvantages, so it's important to consider factors such as cost, performance, and maintenance requirements when choosing the right battery for your solar power system.

Lead-acid batteries are the most common type of battery used in solar power systems. They are relatively inexpensive and have a long life span, but they can be heavy and can lose their charge quickly if not used regularly. It's common to use sealed or wet style batteries for renewable energy applications. 

The main difference between sealed lead-acid batteries and wet lead-acid batteries is the way in which the electrolyte solution is contained. In sealed lead-acid batteries, the electrolyte solution is absorbed into a sponge-like material, whereas in wet lead-acid batteries, the electrolyte solution is held in a separate compartment within the battery.

Sealed lead-acid batteries are also known as "maintenance-free" or "valve-regulated" batteries because they do not require regular maintenance or the addition of electrolyte solution. Wet lead-acid batteries, on the other hand, require regular checking and topping up of the electrolyte solution to ensure that the battery remains in good working order.

Sealed lead-acid batteries are generally more expensive than wet lead-acid batteries, but they are more convenient to use and require less maintenance.

Lithium-ion batteries are becoming increasingly popular for use in solar power systems because they are lightweight, have a high energy density, and can hold their charge for a long time. However, they are also more expensive than lead-acid batteries.

Nickel-metal hydride batteries are similar to lithium-ion batteries in that they are lightweight and have a high energy density. They are also relatively inexpensive, but they may not last as long as lithium-ion batteries.

The team here at SolarPanelStore.com has been working with batteries for off-grid and grid-hybrid systems for many years, and we have a lot of experience that we are happy to share with our customers. Please feel free to contact us for questions about batteries or to help with any kind of solar application!

Solar Batteries 101

Solar Batteries 101

Do I need solar batteries for my system?  

 Everyday we talk to customers looking to use solar energy to power all kinds of different things. For instance, if they want to simply reduce their electric bill from the local utility, then we're clearly looking at a "grid-tied" solar system. But often people want to power some type of device directly from a solar panel. Or they need mobile power, or power for something remote and away from electric utility lines, or back-up power. More often than not, this means batteries! And not just any batteries, but solar batteries (batteries suitable for solar systems).

 Can't I just plug it directly into a solar panel? 

Usually no. Most devices that need electricity require steady, reliable current (amps) and voltage to operate as designed. The voltage produced by a solar panel when it captures the sun's light varies constantly. Clouds, weather, and the changing position of the sun throughout the day are to blame. Also, solar panels only produce DC (direct current) electricity, which means it must be inverted to AC electricity by way of an "inverter". But an inverter requires steady, consistent energy as well. However, there are a few types of "loads" that can be powered directly from a solar panel. Certain types of attic fans or water pumps can operate effectively with the varying voltage throughout the day. But for most other loads, the DC energy from the solar panel must be first inverted to the proper form or stored in a solar battery system.

What what is a battery, really? 

Putting solar aside, for a moment, we are all familiar with batteries. We use all kinds to power all kinds of devices. But at the end of the day, a battery is simply a device to store energy produced somewhere else at some other time. Like a water storage tank filled by a pump, a battery holds or stores a certain amount of energy.

How much depends on the battery's size, construction, type, chemistry, environment, etc. Unlike the throw-away AAAs in your TV remote, batteries used for solar energy systems big and small are rechargeable. A rechargeable battery can be discharged and recharged over and over again (one discharge and recharge is called a "cycle"). The battery's chemistry and type determine how deeply the battery can be discharged and the number of cycles it can perform during Its lifetime.

Batteries for Solar? 

There are a number of factors to consider when buying solar batteries. Because the battery bank is one of the most expensive components of such a system, it is important to carefully design the battery bank so that it performs as expected for as many years as possible. When designing a battery bank we first analyze how the batteries will be used. How much energy must the battery bank supply to the “loads” each day? A load is any device that uses energy. People are often surprised when we ask them to list all of the loads they will use each day, the watts of each load and how many hours a day they expect to use them. But

that detailed info is needed to determine the daily watt-hours of storage which determines the battery bank size. From there we consider other factors to recommend the best battery bank for the specific situation.

Other factors 

Because we're trying to keep this overview fairly basic, we will discuss factors like battery chemistry, sizes, capacity, and more in later blog posts. But we want to comment on just a couple more important points to keep in mind as you look for solar batteries.


There are quality long-lasting batteries and there are cheap short-lived batteries. We stick with quality brands. You can find cheap batteries all over the place. But if you want your batteries to last and give your solar system the most bang for the buck, it's usually worth it to get quality. We often supply quality brands that are not even on our site today, so please ask!

Deep Cycle 

 For solar systems, you want to stick to deep cycle batteries only. You don't want car or “starting” batteries for a solar system. If the battery doesn't list Amp Hours and instead only lists CCR (Cold Cranking Amps) then avoid it, even if the battery is labeled Deep Cycle. Deep cycle batteries are meant to slowly discharge down to a certain point and then recharge fully. And repeat that cycle over and over for many years. Car batteries are designed to a very different thing--quickly start a car engine in a short burst of current. Just remember deep cycle.


Because solar battery systems store energy for gradual discharge (usually throughout the night), a good deep cycle battery will list its storage capacity in Amp Hours as measured over a 20 hour discharge rate (designated as "C/20"). Sometimes batteries will show different discharge rates (C/100, etc). Just make sure to use the C/20 rate to compare capacities among batteries. The more amp hours the better. Deep cycle batteries generally should not be discharged beyond 50% of its rated capacity. If they go beyond that level, the battery can be damaged and its ability to fully recharge will be reduced. For that reason, it's really important to size the battery bank correctly or else your battery life will be cut way short.


 If you are running an RV solar system, boat system, outdoor yard lights, water pump, remote instrumentation, etc., then chances are very good that you are operating equipment designed to run on 12 volts of DC electricity (sometimes designated VDC). So you will want to keep your battery bank at 12 volts. If you are powering a large off-grid home, then you'll want to be at 48 volts. Smaller cabins at 24 volts. We design battery banks to match these system voltages by using individual batteries that may be at 12 volts, 6 volts or 2 volts. Again, we'll get into the specifics in a future post, but for now that is why you'll see batteries with these different voltages listed on our site.


While there is a lot of hype today about lithium ion batteries, lead acid batteries still lead the way as the most economical, long-lasting battery for solar energy systems. For most people, lead acid batteries still make the most sense. But if the batteries need to be light, fully cycle daily, and at moderate temps, then lithium may be a great choice. If price isn't a big deal. But today, lithium prices are pretty high compared to lead acid.

Click here to see our lines of batteries for your application.  Questions, just ask!


Battery Maintenance

Battery Maintenance

Battery Maintenance

To get the most life and performance out of your solar system's batteries, regular battery maintenance is key.   In this article we cover some basic principles of flooded deep cycle battery maintenance. Please keep in mind all battery systems are different and you should consult your battery data sheet for information specific to your batteries.

Battery Basics.

Voltage.  What is your battery bank voltage? Typical battery voltages include 12V, 24V and 48V, 36V is also found in some instances. Remember that series wiring (positive to negative) will increase voltage while keeping amperage the same. Parallel wiring (positive to positive and negative to negative) will increase amperage, while keeping your voltage the same.

Battery Type. What type of battery are you using? Common battery types include deep-cycle flooded, AGM and gel batteries. Lithium batteries are not yet as common for off-grid applications due to the cost, but they are becoming more popular. AGM, Gel, and Lithium batteries are sealed,  maintenance-free, and more expensive than flooded deep cycle batteries.  Because this article is about battery maintenance, we won’t focus on these other battery types.

Capacity.  Battery capacity for solar systems is measured in amp hours based on a C/20 discharge rate.  The faster a battery is discharged, the less capacity it has.  C/20 is a slower discharge rate that approximates the typical discharge time period of a solar system.  While amp hour capacity can vary by the battery case size, it is common to see 12 volt batteries around 100 amp hours and golf cart style 6 volt batteries around 225 amp hours and L16 size 6 volts around 400 amp hours.  Also if you convert capacity into watt hours you can better estimate how much capacity you need to power the loads you have.  Because Ohm’s law tells us that watts = volts x amps, a 12 volt 100 amp hour battery is 1200 watt hours.  Because the maximum discharge level for deep cycle batteries (“dept of discharge”) is generally 50%, that means that a 1200 watt hour battery only has 600 watt hours of usable capacity.

Tools.  Below is a list of tools you’ll need to do your battery maintenance:

  • Eye protection
  • Gloves
  • Wrench
  • Voltmeter
  • Baking Soda
  • Battery Post Cleaner
  • Distilled Water
  • Hydrometer
  • Vaseline
  • Notepad

Visual Inspection.

The first step is a visual inspection.  But before you do,  ALWAYS be sure to wear eye-protection and gloves when working on a flooded deep cycle battery bank!  And wear old clothes!

A visual inspection includes checking all the batteries. Be sure to look for cracks or irregular bulges. Check for any fluid on or around the batteries. Cracked or leaking batteries will need to be replaced. Also be sure to inspect cable lugs and battery terminals. These should be clean of fluids, dirt and corrosion. Inspect cable connections for tightness.  All connections should be at the proper torque value, which can be found in your battery’s data sheet. Be sure to not over-tighten connections as this can lead to battery damage and hot spots. While connections that are too loose result in poor conduction and hot spots.

Make regular visual inspections of your battery bank a habit. Early problem detection can save a lot of time, money and headaches down the road. Shoot for monthly inspections until you get a good idea of how your batteries perform. Over time you may find that monthly inspections are too frequent, or not enough!  How frequent really depends on how hard they are working.  

Battery Tests.  

After you finish visually inspecting your batteries, there are two important tests you should do as part of regular maintenance:  1) Open Circuit Voltage Testing and 2) Specific Gravity Testing.  Performing these tests each month will provide you with important information about your batteries’ health, age and charge level.  They will also help you detect problems like overcharging, undercharging and overwatering. Finding these issues early is key to keeping the entire battery bank strong.

Specific Gravity.

Testing the specific gravity of a battery’s electrolyte solution with a hydrometer is an accurate way to measure a battery’s “State of Charge”.  As a lead acid battery discharges, sulfuric acid floating in the electrolyte binds back to the charging plates (forming lead sulfate), which makes the electrolyte more water-like and less dense and causes the Specific Gravity to go down.  The reverse is true when the battery charges (Specific Gravity goes up as lead sulfate from the plates changes to sulfuric acid in the electrolyte solution).  Also if your battery’s electrolyte level gets too low, the density goes up and Specific Gravity goes up.

  1. Don’t add water at this time, If your batteries are low on water you should add water and let them go through a complete cycle before testing.
  2. Fill and drain your hydrometer at least 3-4 times before taking your test sample.
  3. Take a sample, you should have enough liquid to completely support the float.
  4. Take a reading and record it. Return the sample to the cell.
  5. Move to the next battery cell and repeat the above 3 steps.
  6. Be sure to check all the battery cells.
  7. Replace all battery caps and clean any liquid that may have spilled in the process.
  8. Correct the readings to 80 degrees fahrenheit by: 
  9. Adding 0.004 for readings 10 degrees fahrenheit below 80 degrees
  10. Subtract 0.004 for readings 10 degrees fahrenheit above 80 degrees
  11. Compare the readings.
  12. Check the state of charge using the below table.

Readings should be at factory specifications of 1.227 +/- 0.007. If any specific gravity is reading low follow the below steps.

  1. Check and record voltage levels.
  2. Put batteries on a complete charge.
  3. Take specific gravity tests again.

If after reading specific gravity you find cells registering low you may try the below steps.

  1. With your voltage meter check voltages again.
  2. Proform an equalization charge.
  3. Take specific gravity tests again.

After your equalization charge has finished and your still getting lower voltage readings than factory specifications you may have one or more of the below conditions:

  1. The battery was left too long in a state of discharge.
  2. The battery was over-watered during the last maintainence procedure.
  3. A weak or bad cell is developing inside the battery.
  4. Electrolyte was spilled or has leaked from the battery.
  5. The battery is reaching the end of its life.

If you are showing signs like those above you may want to take your battery in to a specialist, or consider replacing the battery.

Open Circuit Voltage.

When testing open circuit voltage,  batteries should remain idle with no charging or discharging for 6 hours.  It is best to let them sit idle for 24hrs.

  1. Disconnect all loads from batteries.
  2. Measure voltage using a DC Voltmeter (or a Multimeter set to DC voltage)
  3. Check battery state of charge with the below table.
  4. Charge the battery if it registers 0% to 70%

If your batteries are registering below the table 1 values, the batteries may have been left too long in a state of discharge, or the battery may have a bad cell. In this case it is best to take the battery to a specialist or replace the battery.

Battery Watering.

All flooded batteries use distilled water as a key component of their electrolyte solution.  While not everyone loves checking and adding water to batteries, because flooded batteries are a lot less expensive than sealed batteries, it is worth doing, and doing right.  There are some battery watering products on the market today such as the Trojan Hydrolink, and the BWT system by US Battery that are not within the scope of this article, but make the battery watering process easier and quicker.   

Distilled water should be added after the battery has been fully charged.  However, the water level should at least cover the battery plates before charging. That will ensure that the water levels are sufficient during the different states of charge.  Also, keeping your battery plates covered will keep them from being exposed to air, which can cause corrosion to the plates.

It is also important not to overfill the batteries with water.  Overfilling can result in the battery overflowing and losing battery acid which will degrade the capacity of the battery. Battery acid is a highly corrosive liquid and can cause damage to anything it touches. Battery containment trays can help avoid damage as they provide a safe place to catch any overflowing acid-containing electrolyte. You should use a distilled or deionized water for watering because these liquids have very low mineral counts. Because the battery electrolyte is a mixture of water and battery acid, always wear protective gloves and eye protection when handling or maintaining batteries to protect your skin and eyes from damage.  It’s also best to wear old clothes!

Steps to adding water to a battery:

  1. Put on your protective eye protection and gloves.
  2. Remove vent caps and check the inside fill wells.
  3. If the battery plates are exposed add just enough water to cover these plates.
  4. Put your batteries on a complete charge before adding any additional water.
  5. After your batteries are have finished charging open vent caps and check the fill wells.
  6. Add water until the water level is about ⅛ below the bottom of the fill well.
  7. Clean and replace the vent caps.

You should never add battery acid to a battery.

Below is an example of the Trojan Battery fill wells and where your water level will need to be.

Battery Cleaning.

Regularly cleaning your battery terminals ensures that current will flow through your battery bank smoothly which, in turn, helps make sure all your batteries receive an equal and full charge.

Steps to battery cleaning.

  1. Put on your eye protection and gloves.
  2. Make sure all vent caps are tight.
  3. Clean the battery tp with a cloth or brush with a solution of baking soda and water.
  4. Clean battery terminals and lugs with a post cleaner.
  5. You may want to use a protective coating of anti-corrosive spray or silicon gel.
  6. Clean the area around the batteries this should be a dry organized area.

Keeping a small notebook as your maintenance journal can be helpful to record your maintenance dates and test results so you can compare readings and determine the best maintenance schedule.

Batteries and Solar.

The goal with any battery-based solar system is to maximize the health and life of your battery bank.  Why?  Because the battery bank is often the most expensive component of your system.  So be sure to charge your batteries completely after use. Batteries that are not fully recharged soon suffer from reduced charging capacity and a shorter life span.  If you are going to store the batteries for an extended period of time you will want to charge them fully every three to six months. Flooded batteries can be expected to self-discharge up to 15% each month. This self-discharge rate can depend on the age of the batteries and also the temperature they are stored at.

It is also important that you size your solar array to be large enough that it will fully recharge your battery bank in 4-5 hours during an average sunny day.  That will help your battery bank stay fully charged as often as possible to ensure long battery life.

We hope you found this article helpful.  Following these recommendations should help you keep your deep cycle, flooded batteries healthy and extend their life and your investment for years to come.

Can I DIY Solar?

Can I DIY Solar?

DIY solar?  Do-it-yourself?  Really?  Let's take a step back first.  You've heard about solar power. And that solar electric (PV) systems save you money.  Solar power is a renewable energy source. It's better for the environment. Good stuff. But expensive right?  First there's the equipment. Then design. Then you need someone to install it all? Whew!

Enter DIY Solar.   Can't you save money and install a solar electric system yourself? Yes you can! Is it for everyone? No it isn't. For example, don't we all know someone who changes their own brakes? Disks, rotors, pads, calipers. What did your last brake job cost you? $1000? Do you think your buddy saved some cash doing the brakes himself? You bet he did. Probably 50% less than an auto dealer break job. But not everyone knows enough, is bold enough, or mechanically-skilled enough to tackle that job. But many could.

The point is, for people with some DIY experience, some mechanical inclination, some drive to learn and courage to try, installing much of a solar electric system is quite do-able. In fact, we estimate more than half of our customers install the majority of their solar systems DIY. While it is pretty common for them to hire a licensed electrician to perform the final wiring connections of their system to the utility grid (and recommended and often required), they often tackle the rest themselves. And like the backyard mechanic  . . . they save a bundle!

System types.  

If you are reading this article, then you've probably learned that there are different types of solar electric (or solar photovoltaic—PV) systems out there. And some are easier to tackle DIY than others. Systems that are less complex and/or smaller are good PV systems to cut your teeth on. For example, many of our DIY house system customers got their feet wet in solar by putting a system in their RV. On the other hand, a basic residential grid-tie system, while not necessarily small, is quite straight forward compared to designing and installing a completely off-grid or hybrid grid-tie/battery-backup system.  Let's compare these different types of solar systems:

Grid-tied systems. With solar's popularity boom in recent years, grid-tied PV systems are the most popular systems,and the most straight forward to design and install. Since these systems simply make DC electricity from the sun and convert it to AC electricity to power your house (and sell excess energy back to the grid), batteries don't enter the picture. And that reduces complexity. No charge controllers, special inverter-chargers, additional shut-offs, sub-panels, etc. Instead, solar panels are simply wired to inverters which are wired to your house's electric panel and a new meter that measures what is sold back to the grid.

Off-grid system. Instead of connecting panels through a smart grid-tie inverter that routes inverted AC electricity where it needs to go (house vs grid), an off-grid system means batteries.  The battery bank is usually larger than you expect (although it does vary depending on the size of the load) and needs to be sized correctly to power the home or loads as desired, while maximizing the life of those expensive batteries. But the DC electricity from the panels needs to first charge those batteries via a DC solar charge controller. DC electricity from the panels (if batteries are full) or from the batteries (if sun isn't shining) then flows though the inverter/charger to feed AC electricity to the house's AC loads. When the sun doesn't shine for 2-3 days, the inverter/charger fires up an attached generator to charge the batteries up. More components, more going on, more to learn.

Hybrid System. In our opinion, this is the toughest, most complex and most expensive system to build. Well, short of an AC-coupled system anyway (beyond the scope of this article!). In this hybrid model, components and considerations of a grid-tied system blend with those of a battery-based system.  Hybrid systems have traditionally been used to add battery-back up to power certain critical loads when the grid goes down.  Instead of using a generator, a battery bank is kept charged and ready by the grid, but then get's refilled by the solar array once the grid fails.  Hybrid systems are increasingly used in situations where the excess power cannot be sold back to the grid (Hawaii) or net metering is prohibited or inhibited by the utility.  In those cases, battery storage is added to a system to power loads at night and essentially only use grid power for backup.  In any event, with the combination of grid and battery components, system-design gets pretty complex and tougher to tackle DIY.

Next steps to DIY Solar.  

Now that you understand the types of systems and some of the complexities involved, let's look at next steps in your DIY Solar journey:

Know your goal.  This is basically the step we covered above.  Understand what you want your system to do.  Do you want to cut your utility bill by 100%? 50%? Look at the last 12 months of utility bills to get a feel for how much energy you want the system to produce.  Are you just looking to power a small system like a remote water pump? Or power a gate?  Knowing your goal is the first step.

Get educated.  Learn, learn, learn!  Subscribe to Home Power Magazine's digital archive service for great articles to help you DIY Solar.  You can find them at www.homepower.com.  Keep checking back here on our site (www.solarpanelstore.com) and our sister site (www.cosolar.com) for a current and growing list of articles and blog posts on all kind of solar topics.   A good forum to read or post questions  on is www.solarpaneltalk.com. Getting informed will help you plan the system for you  and learn what questions to ask when you call an expert

Seek Expertise. You will need help designing your system! There are lots of considerations and nuances for your location and goals. As part of the buying process, at SolarPanelStore.com we regularly help our customers think through the options and help design the right system. Because we don't install systems, we do recommend hiring a local, licensed electrician or solar installer that can help you with final wiring connections or other parts of the project as needed.  Know your limitations and find those folks up front

Permitting/Requirements. Every state and utility (and HOA) is different, so start early to understand what requirements your local utility and AHG (authority having jurisdiction)  have for your system. For example the utility may limit the size of your PV system to a percentage of your historical use.

Incentives. While there are common national programs like the Federal Tax Credit (FTC) and USDA's REAP (Rural Energy for America Program) program, each state and utility have different programs as well. Go to www.dsireusa.org to research what's available to you.

Buying equipment. Buy good equipment from someone who knows what they're doing. We expect reliable, consistent electricity service from the utility, and you'll want the same for your system. We get calls from people buying cheap on Amazon or Home Depot, but then need help but things don't work and they can't get help from those sellers. Since 2002, we at SolarPanelStore.com have worked with our customers all the way through their projects, from concept to maintenance, answering questions, providing advice, pointing to resources and working with manufacturers. And we work hard to be competitive with the bigger guys that don't call you back. You get what you pay for.

Tools. You'll need typical tools used in any home remodeling project, plus some electrical and wiring tools as well. Like an MC4 connection tool, or a Digital Multi Meter to test for voltage and polarity. Again we at SolarPanelStore.com can guide you.

Safety. Obviously solar electric systems involve electricity, which if not handled correctly can cause serious injury or even death. Solar PV systems can involve dangerously high DC current, so taking safety seriously is very important. And lifting large solar panels and mounting them atop poles or roofs involves ladders and risk of falls.  So get familiar with good safety practices described in articles at Home Power.

By no means is DIY Solar a piece of cake.  But with some skill, courage, willingness to learn, and keeping these points in mind, you're well on your way to going solar!