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Sealed batteries Vs Flooded batteries

Updated: Jun 12, 2023

Both sealed and flooded are members of the lead-acid battery family. Both batteries are rechargeable and use chemical reactions to store electricity. However, flooded batteries are one of the oldest and most popular versions of lead-acid batteries and available since 1859. On the other hand, sealed batteries are developed in 1930.

Sealed batteries are also called Maintenance-free batteries or Valve-regulated lead-acid (VRLA) batteries or Sealed Maintenance-free (SMF) batteries.
And Flooded [FLA] batteries are also called Wet batteries.

Besides lots of similarities, there are lots of differences between both types of batteries. And in this blog, you will all the differences between them.

Sealed Vs Flooded battery

The electrolyte of flooded batteries is in liquid form and required a regular water level up. Whereas the electrolyte of sealed batteries is gel form or acid-socked glass mat form. Hence sealed batteries don’t require any water and these batteries can be placed upside down or on their side.

1. There are two versions of sealed batteries available, the AGM [Absorbent Glass Mat] battery and the Gel battery.

2. Sealed batteries have a low self-discharge rate as compared to flooded batteries. Flooded batteries have a discharge rate of up to 15% per month. Whereas sealed batteries have a 1-3% of discharge rate.

4. Sealed batteries are more expensive than flooded batteries.

5. Sealed batteries are spill-proof/leak-proof, hence also called non-spillable batteries. And this makes them easy to transport.

6. Flooded batteries have a high energy density, whereas both types of sealed batteries have a low energy density.

Energy density means the amount of energy stored in the battery of a given size or weight.

7. Sealed batteries have high power density than flooded batteries.

Power density means the peak amount of power discharged from the battery in a given time.

8. Flooded batteries required periodic water placement, whereas sealed batteries are maintenance-free. Hence also called a Sealed Maintenance-free [SMF] battery.

9. Sealed batteries have high round-trip efficiency. Flooded batteries have round tip efficiency of 70-80% and sealed batteries have round trip efficiency of 80-90%.

During charging and discharging, energy is lost in the form of heat. And this efficiency penalty is called Round trip efficiency.

Sealed vs flooded battery which is better

For long power cuts, ideal conditions, steady load, and low power appliances standard flooded batteries are the most economical battery. However, for harsh conditions [like cars and boats] or less frequent power cuts sealed batteries are far much better than flooded batteries.

Standard flooded batteries are sufficient for low power appliances, however, for heavy power appliances, deep-cycle flooded batteries are best.

In a developed country, where power cuts are very rare and the duration of power cuts is in minutes. You will find sealed batteries are much more popular for home backup. However, in underdeveloped countries where power cuts are very frequent and long, flooded batteries are far more popular for home power backup than sealed ones. Due to low cost and high energy density.

Moreover, due to high power density and leak-proof design. Sealed batteries are only used for cars and boats both in developed as well as underdeveloped countries.

Related Blogs:

How to tell if the battery is sealed or flooded

Flooded batteries have water level indicators on top of them, on the other hand since the electrolyte of sealed batteries is either in gel form [GEL battery] or replaced by wicks Glass mat [AGM battery]. So, you won’t find any water level indicators on top of it.

Are car batteries sealed or flooded?

To start a car high power density battery with good performance in cold weather is required. Since sealed batteries are spill-proof, have better power density and good performance in cold weather than flooded batteries. Hence, only sealed batteries are used in car batteries.

Among the two types of sealed batteries, the AGM type is preferable over the gel type. And all car manufacturers use AGM batteries. Learn More, UPS battery Vs Car Battery.

Is a sealed battery really sealed?

Sealed are completely sealed and its electrolyte won’t spill out, even if you placed it upside down or on its side. However, during overcharging it produces gases, and a safety valve is provided to discharge is gas into the air. Hence sealed batteries are also called valve-regulated lead-acid [VRLA] batteries.

Are marine batteries sealed or flooded?

Marine batteries are designed specifically with heavier plates and robust construction designed to withstand vibration and pounding. And the same can be designed by both sealed or flooded types configuration. However, due to safety reasons and extreme conditions. Almost 100% of the marine batteries used are sealed type.

Can a flooded battery be maintenance-free?

The electrolyte of the flooded battery is in liquid form and it contains 80% of water. Also, its self-discharge rate is high, hence it losses water over time. And required time to time water fill up to make is properly work. Due to these reasons

What is the difference between sealed and unsealed batteries?

Unsealed batteries are also called flooded batteries and the difference between flooded and sealed batteries is the same as the difference between unsealed and sealed batteries. The electrolyte of the unsealed is in liquid form and the electrolyte of the sealed is either in gel form [GEL BATTERY] or replaced by an acid-soaked glass mat sealed between battery electrodes [AGM BATTERY].

Is a deep cycle battery a flooded battery?

Deep cycle batteries can be both flooded and sealed type. The difference between the deep cycle and the normal standard battery is the maximum depth of discharge. The normal battery has a 50% depth of discharge, whereas the deep battery has an 80% DOD.

What is a flooded battery used for?

Flooded batteries are used to store power and provide backup during power cuts. These batteries are less expensive than sealed batteries and have battery energy density. These batteries are ideal for long power cuts but required regular maintenance and produce harmful gases.

What is inside a maintenance-free battery?

There are two types of maintenance-free batteries available, that is gel type and AGM battery. Inside a gel-type maintenance-free battery, the electrolyte is in gel form. Whereas inside AGM-type maintenance-free battery, the electrolyte is replaced by an acid-soaked glass mat sealed between electrodes.

Do sealed batteries need water?

The electrolyte of sealed batteries isn’t in liquid form. Either it is in liquid form or replaced by an acid-soaked glass mat sealed between electrodes. Hence there is no need to water filling for sealed batteries. Moreover, you won’t find any water-filling points on sealed batteries.

And that’s the reason, why sealed batteries are also called maintenance-free batteries.


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19 בנוב׳ 2022

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