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How to Tell if a Deep Cycle Battery is Bad – Everything You Need to Know About Replacing Solar Batteries

Updated: July 19, 2023

How to Tell if a Deep Cycle Battery is Bad

No matter what sort of battery you are using, the performance will diminish the more you use it. This is why it is so important to test your deep cycle batteries and make sure they are actually holding a charge.

Even the highest quality lithium-ion deep cycle solar batteries continuously degrade from the moment they are first used. This degradation is an unfortunate, but unavoidable consequence of the chimerical reactions that occur inside batteries when they are running.

The rates of degradation will differ depending on a wide variety of factors, including the storage conditions for the battery itself, external temperature variations, the overall quality of the battery, and the amount it is used. This is why no deep cycle batteries list an exact expiry date. While some will have total recharge cycle estimates, you cannot rely on these numbers completely. 

How Can We Help?

To help you keep an eye on your deep cycle solar batteries and make sure that your solar battery bank is operating as it should, we are going to explain how you can tell if a deep cycle battery has gone bad.

We will also recommend some high-quality solar batteries and solar kits you can use to build a high-performance battery bank for your solar power system.

Three Ways to Check if a Deep Cycle Battery is Bad

If you have noticed that your solar battery will no longer hold a charge, there are three simple ways to test the battery. While you might just assume that any battery that is not holding a charge is bad, the truth is there could be a number of other reasons why you cannot access power from your battery bank. 

In some cases, people blame their batteries when the reality is their solar panels are underperforming. In other cases, your batteries could be losing their charge due to battery drain, which occurs when power flows in the reverse direction from your battery to your solar panels. Often, this is the result of using a poor-quality or faulty charge controller. 

This is why it is always worth testing your deep cycle batteries to make sure they are bad, before you go about replacing them. The following are three of the most accurate and straightforward ways you can test the status of a deep cycle battery:

  1. Perform a Thorough Visual Inspection of the Deep Cycle Battery

In many cases, a thorough inspection of the battery will be enough to tell you if it is bad. Even if you are fairly new to solar storage and you do not know much about deep cycle batteries, there are some obvious signs that your battery could be faulty. Check for the following:

  • Broken or loose terminals
  • Any sort of bulging in the battery’s case
  • Cracks or ruptures in the exterior of the battery
  • Leaks or pools of liquid around the battery
  • Significant discoloration

Searching for the above signs of degradation should always be your first step if you suspect your deep cycle battery might be bad. For starters, a broken or loose terminal can become dangerous if the battery continues to be used, as these issues can lead to short circuits.

When a short circuit occurs, all of the power stored in the battery is unloaded instantly, which can damage any solar equipment that is connected to the battery, and, in some cases, the battery can become extremely hot and even explode.

Bulging in the case is typically a sign of overcharging, which could mean you have an issue with your charge controller. Cracks, splits, holes, and other obvious signs of wear could mean your battery is degrading to the point that it is becoming unsafe to continue using. Some types of deep cycle batteries will fail if they have leaked too much fluid, as a lack of fluid exposes the plates within the battery’s cells to oxygen, which can lead to sulfation. Sulfation will cause a battery to fail early, so large-scale leaks of dark colored fluids is almost always a sign that your deep cycle battery is in need of replacement.

  1. Perform a Voltage Reading on Your Deep Cycle Battery

Checking the voltage of your battery is a reliable way to tell if it can still hold a reasonable charge. 

To get an accurate voltage reading, you will need a digital multimeter, or DMM, which is a simple and affordable device that will allow you to measure the electrical values of a battery, meaning the voltage (volts), current (amps), and resistance (ohms). They are affordable and can be found at most hardware stores. 

You should know the normal voltage for your battery, but if you cannot remember, it should be listed on the side of the battery. Most solar battery banks use 12-volt deep cycle batteries, but it is still worth checking before you take a reading.

If your battery reads 0 volts, there is a good chance it experienced a short circuit. If it cannot reach higher than 10.5 volts while being charged, it likely has a dead cell. If you get a normal voltage reading, but the battery still will not hold a charge, it could be sulfated and it would need to be replaced. 

  1. Load Test the Deep Cycle Battery 

Performing a load test is a little bit trickier, but it is an accurate way to tell if a deep cycle battery is bad. While it is possible to perform the test at home, you can also just take your battery to a local automotive shop. Most shops will be willing to test your battery for a small fee, which would let you know if you need a new battery. 

You can also purchase a battery load tester at most hardware stores and auto parts shops. When performing a load test, you would remove all battery cables from their terminals and hook up the load tester. You would then use the load tester to apply 15 seconds of a load equivalent to 50% of the battery’s CCA rating. You would then refer the minimum passing voltage according to your load tester, which would give you an idea of the condition of the battery. If the test voltage is below the minimum passing voltage, the battery is bad and needs to be replaced. 

Replacing and Purchasing Deep Cycle Batteries

While it can be annoying, replacing deep cycle batteries that have gone bad is just a necessary part of running a solar battery bank, as all types of batteries degrade over time. Fortunately, solar battery technology continues to improve and high-quality deep cycle batteries are more efficient and affordable than ever before. 

No matter what your power storage needs are, you will find high-quality replacement batteries by shopping our Deep Cycle Solar Battery Collection. We carry a massive selection of deep cycle batteries from some of the most reputable brands in the entire solar industry.

Final Words

Before you rush out and buy a replacement, check to make sure that your deep cycle battery has actually gone bad. In many cases, what seems like a faulty battery is simply just a disconnected wire or a performance issue somewhere else along the line in your solar power system.

By performing the three tests outlined above, you will be able to determine if your deep cycle battery has gone bad. If the battery does need to be replaced, you can find a high-quality replacement at a competitive price by shopping our deep cycle solar battery collections.

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Article by

Max Bair Marshall

Max is a co-founder of Shop Solar, a company that he established in 2018 to revolutionize the solar industry by simplifying the process and making it more simple and cost-effective. Under his strategic leadership, Shop Solar has grown into a comprehensive one-stop-shop, empowering over 40,000 customers to access top-quality solar and storage solutions, comprehensive information, intuitive tools, and professional installation services.

With a passion for innovation and sustainable energy, Max has successfully expanded the business's reach and impact, serving as a driving force in the company's growth and development. Today, as the leader of a dedicated team of 60+ professionals across North America, Max continues to set new standards of excellence in the renewable energy industry, with a mission to transform the way people access and utilize clean energy.

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