What Is a Flooded Battery? The Ultimate Guide


As soon as you hear the words ‘flooded battery’ you may think, oh dear, how much is it going to cost to replace it? You may be surprised to know that ‘flooded’ is a deliberate part of the design, and the concept is 1000s of years old.

Likely, you’re already using several flooded batteries. In this article, we’re going to explain what is a flooded battery. You will also learn about its common usage, and how to maintain it.

Batteries are often forgotten, however, we soon remember them when they don’t work when we need them. Don’t be caught out by the inconvenience of a damaged battery. You don’t have to be a car mechanic or an expert in electrochemistry to safely maintain your batteries; read this article and you will see why.

What Is a Flooded Battery?

A typical example of a flooded battery is a car battery. The ‘flooded’ component of the battery is the fact that the battery uses an electrolyte fluid, in which the battery plates are immersed. This electrolyte or battery acid floods the inside of the battery and provides a medium through which electricity can flow.

The fluid nature of the battery means that the battery should be kept in an upright position. Most flooded batteries aren’t sealed. In contrast, we use sealed batteries in other devices like a torch or portable radio, etc.

Basic Anatomy of a Flooded Battery

A flooded battery is made from a non-metallic container. Inside the battery are several cells. Each cell is like an individual battery, but all the cells add up to create a greater output.

Within the battery, there are 2 electrodes made from different metals such as copper and nickel. The battery is then filled (flooded) with a type of electrolyte. This is a fluid that contains ions with a positive and negative polarity.

Snapshot of the Science

It is very important to note that the battery has two electrodes made from different metal materials. One of the metals will react chemically with the electrolyte and want to give up its electrons, and the other electrode will want to receive the electrons.

As the electrons move through the electrolyte and the electrodes, you get current that will subsequently flow through a device with electrical potential that is connected to the battery.

In the end, the electrolytic fluid will become depleted of electrons. This is what happens when your battery is flat. Some batteries are primary batteries and can only be used once; while other batteries are secondary batteries and can be ‘re-charged’ by reversing the chemical process described above.

Why Use a Flooded Battery?

For one, they aren’t expensive and are reliable. You can also use them in a variety of climates, that is to say, whether it is hot or cold. They can be used with multiple devices.

One of the best examples of a flooded battery is your car battery. This type of battery does well by holding onto its charge for a long time. Not only that, but the battery can be charged efficiently and discharges at a steady rate.

All that said, it doesn’t mean that a flooded battery is right for every use. It isn’t designed to be a constant power source as it will drain quite quickly depending on the electrical load. In contrast, a deep cycle battery will deliver sustained power over a longer period of time.

Principles of Maintenance

Flooded batteries do require maintenance. As the electrolyte and electrodes chemically react with each other they produce a form of gas that is vented from the battery. This means the volume of electrolyte gradually diminishes.

You will need to top up the electrolyte by using distilled water. If you neglect to do this, then the electrodes themselves will deteriorate and the battery won’t be as effective at charging and also offering power.

Design Variation – AGM Battery

AGM means ‘Absorbed Glass Matt.’ This is a design variation on the flooded battery. It is a sort of fiberglass mesh that goes into the battery and absorbs the electrolyte and serves as a wick between the electrolyte and the battery plates. This ‘connection’ allows the flow of electrons as normal.

The advantage of this design is that the electrolyte isn’t a ‘free fluid’ as it is in the flooded battery. That means the AGM battery is more stable and not at risk of spilling its electrolyte. This is the design of maintenance-free batteries.

The disadvantage is that the battery is vulnerable to damage when over-charged or repeatedly under-charged.

Health and Safety Considerations

If you have a flooded battery that needs maintenance by topping it up with water, be aware that within the battery will likely be sulphuric acid. Be very careful this doesn’t splash on you or anything else.

Your battery will also produce some form of gas that needs to be safely vented. Instructions on proper use and location should come with your battery. Make sure to abide by these directions.

Knowledge of Flooded Batteries – Fully Charged

Now you know what is a flooded battery and you’ve learnt about electrochemistry and the importance of maintenance. Flooded batteries aren’t the answer to all battery needs but they’re used a lot.

Now that you’ve read this article, you will be checking your car battery for its fluid levels. Be aware that you may have a sealed AGM battery, in which case, don’t try to prize it open. Don’t stop reading here, you can read other informative articles on our site that fit with your information needs.

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