How to Test a Deep Cycle Battery with a Multimeter

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Did you know that car batteries are specially built to offer a short, sharp burst of power to crank over and start the car’s engine?

Only a small part of the battery’s capacity is utilized, and that is preserved by the car’s alternator. Car batteries have thin lead grids and active material to make the most of plate surface area, presenting better and improved starting power.

Nonetheless, they are not ideal for offering long periods of power. Luckily, deep cycle batteries are here! 

Deep cycle batteries are designed using a denser active material and thicker battery plates to endure repeated charge and discharge cycles. Instead of offering high bursts of power for short periods, they are uniquely created to provide sustained power with a lower current draw over a long time. Recurrent cycling doesn’t cause the same level of damage a car battery would sustain throughout the same usage. 

What is a Deep Cycle Battery? 

Deep cycle batteries, also referred to as solar batteries, offer electrical storage in renewable energy systems. You will need some batteries if you like to use your electricity anytime other than when the system is generating it.

Hence, if your solar array generates more electricity during a sunny day, you will need batteries to access that power once the sun goes down. It might appear counterintuitive but, it’s also true that you won’t be able to use the power they produce during a grid power outage. That’s especially true if you have a solar panel array or wind turbine connected directly to the electric grid without batteries. 

How Does a Deep Cycle Battery Work? 

Deep cycle batteries utilized in renewable energy (RE) systems are different from car batteries, and that difference is essential. RE systems are cyclical by nature: energy is captured and preserved, then consumed later in a regular.

For instance, the energy produced in a battery-based solar electric system by the solar panels is stored in the battery bank. That is then utilized by loads on not-so-sunny days or nights. That recurrent procedure subjects the batteries to a slow, regular charge and discharge pattern. 

Car batteries are not intended to be utilized that way. They could release a huge deal of their stored energy at once. To start the car’s engine, they receive a fast recharge right away from the car’s alternator. They are not intended to recover their charge slowly, as would normally occur in a solar electric system. 

In fact, a car battery in a RE system would immediately diet and should be replaced. Meanwhile, a deep cycle battery can be slowly discharged by as much as half of its capacity and will slowly await gradual recharging. If properly kept, a deep cycle battery could last for at least four to ten years. 

How to Fix Common Issues with Deep Cycle Batteries

Keeping and preserving your deep cycle batteries is vital to guarantee a maximum life span and to avoid potential damage. As such, you should check battery issues at an early stage. Troubleshooting these battery problems is comparatively simple to do on your own with the help of a multimeter. 

It’s important that you thoroughly inspect your deep cycle battery. The batteries’ outside can show early indications of failure. As such, troubleshooting these issues can start with a basic inspection. 

Make sure you check that the battery’s top is dry and clean. A battery covered in dirt and dust could discharge across the grime. Further, make sure you check the battery for loose or broken terminals. They are risky as they might lead to short circuits

Meanwhile, waterlogged deep cycle batteries should be assessed for leaking and hurt battery cases, which might have been produced through overheating and overcharging. That issue will not happen with AGM deep cycle batteries, as those are built with glass mat technology that stops the leak, even when spoiled. 

Normally, holes and cracks won’t stop deep cycle batteries from functioning, but they could be dangerous. As such, we suggest discarding the battery which have significantly damaged battery cases. 

But before you decide to test your deep cycle battery, we recommend testing the battery’s charge when it’s completely charged. Do you often find yourself in a situation where you can’t charge your battery? Let it sit for at least one hour before you test it.

Because of discharging or charging, an uneven mixture of water and acid could arise on the plates’ surface. That marvel is what we call surface charge. It should be removed before you start testing, as it might impact your data.

Further, a surface charge could make a battery look great and vice versa. To eliminate the surface charge, you can leave the fully charged deep cycle battery to sit for just four hours. Make sure that the battery isn’t connected to any battery charge or appliances as that will affect the data. 

How to Test a Deep Cycle Battery?

Here are the important steps you need to follow if you would like to test your deep cycle battery with a digital multimeter (DMM).

  • Check the temperature and voltage capacity of the deep cycle battery. It will normally show the reading of the State of Charge (SoC) of different battery types. Without charging, it will be over ¾, meaning seventy-five percent when it’s in rest position for 2-8 hours.
  • Turn off the fuel supply and turn over the engine with the starter motor for at least 15 seconds. Take the lowest voltage over that cranking.
  • Place the sensor on the end of the red wire coming off the DMM onto the battery’s positive terminal. The black wire sensor must go on the battery’s negative terminal.
  • A fully charged standard deep cycle battery must have an output voltage of at least 13v, a bit higher than the 12v likely to be indicated on the battery’s side. Once it’s charged, test the voltage, and test it again for a few hours later. You probably need a new battery if the voltage reading drops more than a volt or two.

There you have it! Are you now ready to do your own testing to your deep cycle battery? Just follow the steps highlighted below, and you’re good to go. Don’t forget to practice safety at all times. Good luck!

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