UniEnergy Technologies Battery » Flooded vs. Sealed Deep Cycle Battery

Flooded vs. Sealed Deep Cycle Battery

If your car is fully electric, it probably has a lithium battery. And if it’s a hybrid, you may have different batteries for each function, though you can also find a matching hybrid cell. But for typical gasoline or diesel cars, you have a lead-acid battery that’s either flooded or sealed. Today, we’re going to explore the flooded vs sealed deep cycle battery. Let’s begin!

Flooded vs. Sealed Deep Cycle Battery: Difference?


Flooded Lead-Acid

Sealed Deep-Cycle Cell

Price Lower initial cost Higher initial cost
Electrolyte 3:1 liquid electrolyte Electrolyte gel or AGM
Usage Higher spurts for starting Lower streams for running
Maintenance Add water and brush terminals No regular maintenance needed
Lifespan Shorter lifespan Longer lifespan
Recommendation Ignition and limited accessories Low voltage and high demand


Car Battery Chemistry

Your car engine may be powered by fossil fuel, but its internal systems are mostly electric. These include the headlights, indicators, car horn, AC, power windows, and stereo. You also need electricity to ignite the engine. And since you can’t plug your car into a wall socket, cars get their electric current from a car battery. It can be quite bulky, and it does need charging.

But unlike the dry cells we use in electronics, automotive batteries recharge themselves while you drive. So they only need rejuicing every four to six weeks, unless you’ve locked the car up for the winter or your vacation. Car batteries work by causing anodes and cathodes to react, releasing electric current. And most cars have a 12-volt battery with lead and sulphuric acid.

While all batteries have lead plates and electrolytes, flooded cells have a free-flowing liquid bath that moves around the plates. But sealed deep-cycle cells use absorbent materials to hold the liquid in place. The most common are absorbent glass mats made of fiberglass. But in some sealed cells, the electrolyte comes in gel form. These gel batteries are far less messy.

All About Flooded Batteries

In a flooded battery, the outer case holds a liquid mix of sulphuric acid and water. These fluids are mixed in a 3:1 ratio to form a highly conductive electrolyte. The case is made of tough, insulating plastic to contain the electricity within the box. Without this protective case, the current could catch the metal parts of your engine and cook you inside your car!

To make the battery work and generate electricity, lead plates are suspended inside the electrolyte. The plates react with the liquid to release an energy surge that will start your engine. And the driving process produces smaller electric waves that gradually recharge the battery. But even if you’re not using it, the battery will drain when it’s idle for a long time.

Flooded batteries are sometimes called wet cell batteries because of all that splashing liquid. But this feature also contributes to the disadvantages of flooded batteries. Since the fluid moves around so much, it can spill out of your battery terminals and corrode them. This is annoying but it’s easily fixed. Clean the terminals with an old toothbrush or tiny wire brush.

Maintaining Flooded Batteries

You can do this more effectively by dipping the brush in mild household acids like vinegar, or even Coca-Cola. But you could also buy commercial terminal cleaners. When you finish, use a designated terminal spray to prevent further corrosion. You can’t stop it completely, but you can slow it down significantly. Another thing to note is evaporation and drying as you drive.

Remember, your car battery heats up inside your bonnet, so the gases and fluid fumes float away. The lead plates must always be fully covered, so you need to add water occasionally. Once a month or so, take off the battery cap and peep into the holes. If you can see your lead plates, your battery needs more water. Top up the battery with distilled water then wipe it.

The reason you use distilled water is that tap water might have mineral salts and additives that could mess with the electrical functioning of your battery. So the water has to be pure. No chlorine, fluoride, flavor, or fizz. If you don’t have distilled water, just boil regular water then cool the water before using it. As the water cools, cover it to prevent recontamination.

All About Sealed Deep Cycle Batteries

Your car has two types of electrical needs. You want a high-power spurt to start the engine, and you need a slower trickle to support your internal systems e.g. the AC, radio, and power windows. Entry-level flooded cell batteries are sometimes called starter batteries because they can only do that initial surge. But for boats and military vehicles, you need consistency.

These vehicles have features that require a constant flow of electricity, so they use a different type of battery called a deep-cycle battery. Because they were first designed for boats, they’re sometimes called marine batteries. But they’re not just for boats. You can use them in any car that has high-demand accessories like heated seats, professional stereos, or computers.

Because these batteries run continuously – as opposed to flooded cell batteries that are only used when you start the car – deep-cycle batteries need a deeper discharge and a quicker recharge. They also need longer battery life so they can accommodate more on-off cycles as they recharge and discharge. They can be especially useful for cars with a start-stop feature.

The Reason for Sealed Batteries

Cars drive on mostly smooth roads while boats ride on waves that are always moving. So boats face far rougher treatment than cars, and there’s much more vibration. Similarly, the batteries in off-road cars and military vehicles get banged about a lot. If you’re out on the ocean or traveling through a war zone, you don’t have the luxury of fussing under the hood.

For this reason, sealed batteries were developed. The seal keeps the electrolyte from spilling or splashing and damaging the boat or vehicle. This can be a life-saving feature when you’re on the water or in the field with no access to mechanics. Inside the case, deep-cycle batteries are built with extra features to withstand harsher impacts and minimize internal vibration.

Because these cases are permanently sealed, the fluid won’t evaporate as quickly so it’ll last longer. And since you can’t open the lid anyway, you don’t need to water your sealed battery. You can’t extend the battery life with water, so these deep-cycle batteries are customized for longer life. They have vents to release any gas build-up and the battery life is quite extended.

Comparing Flooded vs. Sealed Deep Cycle Batteries

Sealed lead-acid batteries are standard in most contemporary cars. These cars have start-stop functionality and lots of luxurious electronic features. They can be gel batteries or AGM batteries aka absorbed fiberglass mat or absorbed glass mat. But unlike a wet cell battery, a sealed deep-cycle battery is mostly on low voltage, so you do face the risk of overcharging it.

If you ask a salesperson, they’ll push a sealed deep-cycle battery on you. Better margins! But remember, deep-cycle batteries were invented for use in boats and military craft. You don’t need one for school runs or office commutes. That said, modern cars sometimes have enough add-ons to launch a rocket! So if you have one of these cars, you may need a deep-cycle cell.

Not all sealed deep-cycle batteries have a starter function, so always double-check! If you want a sealed cell that can still start your car, ask the vendor for a dual-purpose battery that can operate in both modes. Also, whether you’re buying a flooded battery or a sealed deep-cycle one, be sure to get the right group size or BCI number for your specific vehicular needs.

The BCI is the Battery Council International. It’s an organization of manufacturers and other stakeholders in the automotive space. They developed these group sizes to make it easier for industry experts to design batteries that could cut across different car brands and models. Think of it this way – every car has a slot designated for the battery, but it’s not universal.

The slot is called a battery tray, and some cars have deeper or wider slots. The length of cables differ too, and the position of the terminals. The BCI streamlined these dimensions so you can fit the same battery into varied car brands. To make this easier for drivers who have less technical skill, lots of battery websites have filters for car brand, model, and year.

The Trouble With Sulphation

For an automotive battery to work properly, it needs the right concentration of acids and alkalis. So when the electrolyte evaporates, acid crystals cling to the lead plates which means the current isn’t generated effectively. Adding water balances the pH of your electrolyte. In sealed batteries, this isn’t an issue because the liquid dries far slower for longer battery life.

Also, remember that deep-cycle batteries will release low voltage at a gradual pace. They use a valve to limit the amount of current, which is why they’re sometimes called VRLA batteries. VRLA means valve-regulated lead acid. The term applies to both gel cell batteries and AGMs. With wet batteries, the self-discharge rate is about two weeks, so you need the right charger.

But whether you’re using a wet car cell or a dry one, the sulphuric acid and lead are toxic. When your battery dies, take it to an auto store for recycling. If you have a good pro-rated warranty, you can take the battery back to the store and they’ll give you another one at a subsidized cost. They’ll then return the battery to the manufacturer for recycling or disposal.

Some distributors like Costco or Walmart have battery recycling programs too. If you buy a new battery from them without handing over your old one, you might pay a small deposit in lieu of your battery. You can reclaim that cash later when you bring in your dead battery. This way, you’re less likely to dump it in the trash where it could harm the environment.

Which Battery Suits You Best?

With so many batteries on the market, how can you tell what you should buy? The main area of focus for flooded vs sealed deep-cycle batteries is maintenance. Flooded cells are fine, but they need topping up and have shorter life spans. Sealed deep-cycle last longer but cost more so you should only invest in one if you have deep cycle applications like a start-stop feature.

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