How to Tell if a Deep Cycle Battery Is Bad?

How to Tell if a Deep Cycle Battery Is Bad?

Deep cycle batteries are undoubtedly one of the best power pack choices. However, as excellent as they are, they can encounter issues as well due to handling, storing, outdoor conditions, or age. Knowing how to tell if a deep cycle battery is bad can help you save yours in time or prevent early signs of decline from progressing. 

Knowing your deep cycle battery's condition is crucial to avoid hassle. Imagine being a camper and getting stuck outdoors with no source of power! Make it a habit to check your battery for any issues and save yourself the trouble. Read on and refer to this little guide to help you determine the telltale signs of a deep-cycle battery that has gone bad. 

How to Tell If A Deep Cycle Battery Is Bad?

Not Charging At All

Obviously, a battery that doesn't charge in the first place either needs a repair or a replacement. If your deep cycle battery is like this, the best move would be to do a test and ensure the problem is within the power pack and not on external factors like your battery charger. A battery's charging voltage is a good indicator of its overall condition, and you can easily do this with the help of a voltmeter or multimeter.

Inability To Hold Charge

Is your battery draining faster than usual? This could be a warning sign of underlying issues, especially if accompanied by heating. Make sure to have it checked right away, as this could lead to safety risks such as a fire. It's normal for a battery to be warm, but anything hotter than this is likely dangerous. 

Remember, a fully charged 12V battery should have a 12.7V to 13.2V voltage reading. If you have it completely topped up but the voltage is showing a 12.4V rate or less, this means that your battery is sulfated, which commonly occurs when you leave your battery unused and drained for an extended period. 

Meanwhile, a reading of 0 volts could indicate a short circuit, while not reaching higher than 10.5V while charging is a sign that your battery is dead. This is why knowing how to test deep cycle battery is important as it helps you determine whether something is wrong with the power pack early on.

Slow Down In Performance

Deep cycle batteries are known for their excellent quality, particularly lithium deep cycle batteries like a LiFePO4 battery. If you notice your battery declining in performance, i.e., taking too long to charge or being unable to accommodate its usual load, this could be another sign of decline. 

Physical Degradation

Your deep cycle battery's physical appearance alone will tell you immediately if it's damaged. Inspect it occasionally to see broken terminals, bloating, cracks, leaks, and discolouration. Damaged terminals can cause short circuits, which may lead to an explosion. This is crucial especially for camping batteries and caravan batteries as they’re mostly used outdoors and are more vulnerable to elements. 

On the other hand, overcharging is the usual culprit behind bulges or bumps in your battery's case. Other signs of improper handling would be ruptures or splits. While these don't affect the battery's performance much, they still pose risks on the user's part and should be labelled unsafe to use.

If you're using wet-cell batteries, keep in mind that their water levels should always be maintained. Constant exposure to air may dry out the paste surrounding the lead plates and cause sulfation. Sulfation is one of the most common battery issues. It is called the build-up of lead sulfate crystals in the pores of active material in the battery plates. This is also caused by depriving your battery of a full charge. Lastly, any discolouration, even in one battery cell, makes the entire pack unsuitable for use, indicating that you should replace your battery already.

What Causes Decline in Deep Cycle Batteries?

The most common causes of deep cycle battery issues spring from mishandling. This is why it's crucial to follow the manufacturer's instructions on charging, discharging, and keeping your battery in optimal condition during and after use. Below are some of the top culprits behind a bad a deep-cycle battery:


Leaving your battery plugged in beyond its required charging time or charging at excessively high voltage can lead to permanent damage. It's always best to watch your charging time and use the appropriate charger for your battery chemistry. 

Frequent Discharging

Perhaps one of the best things about deep cycle power packs is their ability to be safely discharged by up to 80%. Conventional batteries can typically be charged down to half of their capacity only, so going for a deep cycle battery means you get a longer runtime too. 

However, if drained too quickly and put to use without a proper recharge, this could affect your battery's lifespan and performance. It's still best to discharge within a considerable level, preferably not any deeper than 50%. 


As mentioned, sulfation occurs when crystals form on the plates inside the battery from idle or drained for an extended period. This is one of the top causes of issues among batteries of all types. To prevent sulfation, it's recommended to recharge your power pack every few months, even if you're not using it regularly. 

How to Test Deep Cycle Battery?

Aside from voltage testing, a load test is another effective way to test your deep-cycle battery's condition. This method can also be done via a digital voltmeter. Simply hold the prongs of your voltmeter to the right battery terminals, press the start button, and see where your voltage drops, too. 

However, remember that before load testing your battery, it should be fully charged and left to sit 12 hours before the procedure. This way, the residual charge is already released, and you'll likely get a more accurate result of your battery's performance. 

Note that a healthy battery should be able to hold 9.6V to 10.5V under the load for 30 seconds. If your deep cycle battery maintains this for only a few seconds and starts to drop gradually or immediately falls to zero, this is a clear sign of a battery problem often referred to as "open-cell." It can be the result of a manufacturing error, sulfation, or overheating and once your battery reaches this level, there's no way to fix it anymore.

Deep cycle batteries are considered one of the best investments for avid outdoor adventurers and homeowners for power backup purposes. It’s no surprise that these are often picked as the best camping batteries, caravan batteries, or even house batteries.

If you're also looking for high-quality yet affordable lithium deep cycle batteries for caravans or homes, check out our collection at Outbax. We have a wide range of LiFePO4 batteries available in different sizes to accommodate varying power requirements, perfect for your next trip exploring the great Aussie outdoors. Shop now!

Last Updated on April 5, 2024

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