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What Is the Difference between Sealed and Unsealed Battery? 

 September 19, 2021

By  Phil Borges

There are a plethora of battery types in the market and each has a unique property that makes it useful for specific applications. But in recent years, one of the major qualifications when it comes to batteries has been whether it is a sealed or an unsealed battery.

A sealed battery, as the name suggests, is sealed against leakage and loss of electrolyte. It can be a gel battery or an AGM (absorbed glass mat) construction. An unsealed battery is one where there is liquid flowing freely in the battery, which also facilitates the easy flow of electrolytes.

But which type of battery is better? It may seem like sealed batteries are the obvious choice, but surely unsealed batteries must have something to offer. If you are intrigued by questions like this about battery choices, the following sections should be able to provide some insight:

Sealed versus Unsealed Batteries

Unsealed batteries, as the name suggests, are the ones that have a combination of water and sulfuric acid in liquid form. They are also referred to as flooded batteries as the liquid is allowed to move around inside the cell without being contained or sealed into a designated area.

This free movement of the liquid is also what allows a freer flow of electrolytes, allowing the battery to get great bursts of power and energy. These are more traditional batteries that are still extremely useful to have as power backups, utilities, etc.

These are also commonly used as car batteries. You may have heard of people purchasing battery water for their cars. That is probably because they have to replenish the water in their flooded battery.

Sealed batteries, on the other hand, are the ones that contain only enough liquid so that the electrolyte can flow easily, but not more. The container is not full of a liquid that is allowed to move freely.

In other words, the liquid is “sealed” so that the handling of the battery is easier. Another name for these batteries is maintenance-free batteries. There are also two main types of sealed batteries—gel and AGM (absorbed glass mat).

The former contains a putty-like material that does not leak, while the latter contains acid-saturated fiberglass mats. While AGM batteries tend to be more powerful, gel batteries last longer. These batteries can be found in motor vehicles like cars and bikes and also have a history of being used in military equipment.

Which Battery Is Better?

Unsealed or flooded batteries certainly require more maintenance than sealed ones. For one, if you move the battery around or if they are not handled properly, you risk the liquid spilling about and possibly even leaking through the battery.

If you shake it excessively, then the battery may get damaged. Additionally, flooded batteries also require maintenance to ensure the appropriate levels of liquid are maintained.

They also need to be used with proper ventilation as you do not want the liquid to evaporate in weather extremities. In colder climates, there is also the danger of the liquid freezing.

Having said that, unsealed batteries are still a great option to use as reserve batteries or for power backup. When used correctly and with care, they can also last a very long time.

As is perhaps evident from the descriptions above, sealed batteries are far easier to maintain. There is no free liquid that threatens to leak. The electrolyte is typically absorbed by the separator and does not require too much water.

This type of battery, therefore, can also withstand different climates and also does not require too much ventilation. However, while sealed batteries tend to charge faster than flooded ones and require far less maintenance, unsealed batteries simply offer greater longevity.

In short, both types of batteries have several pros and cons to their names. It may seem like unsealed or flooded batteries are a nightmare to maintain, but when done correctly, they can last you a long time without needing replacement.

Sealed batteries on the other hand are convenient to use and also the safer option, though they cost more money and do not last as long as flooded ones (handled appropriately) do. Which battery you end up choosing will depend on the specific application for which it is being used.

How Do You Tell if a Battery is Sealed or Standard?

If you are uncertain of whether the battery you are handling is sealed or standard, there are a few ways of finding out.

First of all, check the labels of the battery. Manufacturing guidelines dictate that the battery must be appropriately labeled to avoid any confusion or accidents. It should clearly say “wet cell”, “lead-acid”, “flooded lead-acid” or “liquid lead-acid”.

If the battery is a gel-filled lead-acid one, it will say “gel-filled” on the label, and if it is an AGM lead-acid battery, it should say “AGM” or “absorbed glass mat”, “dry cell”, etc. There are various names that could indicate what type of battery it is, so read the label carefully.

If for some reason, the label is not clear or has faded, then you can even look at the container’s construction. Liquid lead-acid batteries should have a cap on top of the battery. A gel-filled or AGM battery, on the other hand, will have a flat top and should not be opened. The only things you may see on the top are the negative and positive terminals.

You can also try shaking the battery lightly, though you should recourse to this method only if the first two do not work out. If, after setting the battery down you can still hear the liquid moving inside the battery, that is a standard flooded battery.

Finally, if none of these methods seem to be panning out, look up the manufacturer’s model number on the label.

Frequently Asked Questions

Since the handling of a battery can be quite a sensitive task, it is natural to have more questions about these batteries. The following sections will attempt to provide answers to some of these frequently asked questions:

Is My Car Battery Sealed or Unsealed?

A car may have a sealed or unsealed battery, but what is the typical standard across the board is that it will be a lead-acid battery. Regardless of which type of battery your car uses, it will have plates of lead and lead oxide, with the electrolyte stored inside a polypropylene case.

Which battery costs more money?

An unsealed or flooded battery is certainly the more cost-effective option as it lasts a much longer time than its sealed counterparts and is also easier on the pocket. Sealed batteries, on the other hand, may be slightly more expensive but that cost makes up for the convenience the battery offers. You truly do not need to lift a muscle to maintain this type of battery, whereas you may end up spending some money on maintaining a flooded battery.

Which battery lasts longer?

While a sealed battery is certainly much easier to handle than a flooded one and also charges much faster, a flooded battery has a longer life, provided it is maintained and handled with care.

The free movement of the electrolyte keeps the battery juiced up for longer. Having said that, often people do not see the worth in maintaining the battery so much when sealed batteries provide great power, even if for a relatively shorter duration of time.

Which are better, gel or AGM batteries?

Gel batteries have a unique quality of absorbing and using the acid better, allowing better depth of discharge. The gel also ensures great leak protection as compared to AGM batteries. But it is important to recharge a gel battery correctly or you can risk permanent damage to the gel material, which can, in turn, corrode the plates.

AGM batteries are comparatively cheaper and longer lasting than gel batteries. They also function better at lower temperatures and are great for utilities like snowmobiles. While both batteries have their pros and cons, it is the application that will decide which battery is better.

About the author

Hi, I'm Phil Borges.. thanks for reading.. My wife says I can't shut up about batteries so to save my marriage I've started this blog .. where I'd be ranting about batteries! Please leave a comment if you have any questions, I'm happy to help!

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