What is a 120ah deep cycle battery? Everything you need to know.


A battery is just a battery, right? They store energy and release energy as needed. Not really. There are several different types of batteries, each with its positive and negative…puns. Before choosing a battery type, consider the purpose for which you will use it. One battery type is more suitable for your specific purpose than another.

In this article, we will dive into the world of 120ah deep cycle battery. We will understand what they are and what they are used for.

120ah Deep cycle battery vs starter battery

Deep cycle battery vs starter battery

The starter battery is the sprinter in the battery world. They are designed to provide a lot of power for short pulses. The point is usually to provide the power needed to start something (such as a motor) and then run it on gasoline.

They are designed to not discharge too much before charging, and deep discharge will damage the life and performance of the battery. This is the type of battery you can find in a car. After the motor starts, the alternator starts to charge the battery until it is fully charged.

However, this is not the only application for batteries. Sometimes you need a battery that can supply power continuously for a long time, for example to run an electric car.

These are deep-cycle batteries-marathon runners in the battery world. They are not short bursts of high power, but provide less power, but last longer. Here, batteries are used instead of gasoline to drive the vehicle.

These are deep cycle batteries-marathon runners in the battery world. They are not a short burst of large power, but provide a smaller amount of power, but the duration is longer. Here, batteries are used instead of gasoline to drive the vehicle.

However, you may be wondering whether both of these functions exist in one unit. In short, yes, they do. This is the so-called dual-purpose battery.

Dual-purpose batteries can handle start-up and cycling, making them an excellent choice when you work with a small size. They provide strong starting current to facilitate starting, and provide low current consumption services to provide reliable auxiliary power.

Discharge capacity

As mentioned earlier, deep discharge of the starter battery will impair its performance. However, deep-cycle batteries are not only designed for long-term power supply, but can also release more stored energy.

The amount of power you can safely discharge varies from battery to battery. Some batteries can only discharge 45% of the energy reserve, while others can safely discharge up to 100%.

Be sure to check the manufacturer’s recommendations for your specific battery.

Uses of deep cycle batteries

We have already touched on the fact that the familiar car battery is the starter battery. So what is the use of deep cycle batteries? Generally speaking, for anything that requires continuous power supply for a long time.

Types of 120ah deep cycle battery

There are also several types of deep cycle batteries. Although they perform the same function, the materials used to make the battery vary. Therefore, different types of deep cycle batteries have their own advantages and disadvantages. Let us look at the main content here.

Flooded lead acid

Flooded lead acid

This is the oldest battery type still in use. Also called a wet battery, the name comes from a battery with a liquid electrolyte inside, which is composed of water and sulfuric acid. If you have ever worked on an old car, you may be familiar with sometimes having to open the tab on the top to add water to the battery. Deep-cycle, flooded lead-acid batteries, water need to be added more frequently.

Due to the liquid, these batteries must always be kept upright. They also need good ventilation. The battery produces hydrogen, and it must have a way to escape. It is not uncommon for the electrolyte to spray out from the vents during charging, leaving acid residues on the battery cover or even on the battery tray and vehicle chassis.

In general, flooded batteries require the most maintenance, including: adding water, cleaning the battery cover, terminals, and surrounding acid residues.

These types of batteries are also heavy when considering the ratio of the weight of the battery to the energy it provides.

For these and more reasons, their popularity is declining.

Valve Regulated Lead Acid (VRLA)-Gel and AGM

Valve Regulated Lead Acid (VRLA)-Gel and AGM

Gel and AGM batteries are other types of lead-acid deep-cycle batteries, but with great improvements. There is no free-flowing liquid electrolyte in them, so there is no need to add any water. However, they are more expensive, and in more demanding applications, their service life is usually not as good as flooded batteries.

In contrast, gel batteries use gel electrolytes, while AGM batteries use electrolytes absorbed in glass matt. If they are used and charged correctly, they will not release any gas, but if they are overpressured, the safety valve will open and release the buildup. Therefore, they do not have to be kept upright and almost eliminate any spillage, reducing corrosion problems common in submerged varieties.

They are very suitable for boats, recreational vehicles, etc.



As far as deep-cycle batteries are concerned, lithium-ion batteries are likely to be the trend in the future. They require no maintenance, can discharge deeper without affecting their service life, and charge much faster than other types of batteries.

Due to the high upfront costs, their popularity has not soared as quickly as you expected. In fact, their service life is much longer than that of lead-acid batteries, and in the long run, they can actually make their prices similar or even cheaper.

Compared with their lead-acid predecessors, they have many other benefits. They are light in weight, can provide rated capacity at any discharge rate, they will not be damaged by placing or operating in a partially charged state, they provide more power throughout the discharge cycle, and so on.


Due to the inherent chemical properties of lead-acid batteries and lithium batteries, their capacities vary greatly. The main difference lies in the relationship between their capacity and discharge rate. Regardless of the discharge rate, lithium batteries can provide up to 100% of the rated capacity. Lead-acid batteries provide significantly less usable energy and a higher discharge rate. Although both battery types may lose capacity in colder weather, the performance changes of lithium batteries are much smaller. For example, at 0°C, the capacity of a lead-acid battery is reduced by up to 50%, while a lithium iron phosphate battery loses only 10% at the same temperature.


The life of a 120ah deep cycle battery is affected by several factors. Compared with lithium batteries, there are more factors that affect the life of lead-acid batteries. In other words, lead-acid batteries are more likely to be abused. Proper maintenance can prolong the life, and can also be discharged and charged correctly. Regularly watering, over-discharging, over-charging and under-charging lead-acid batteries will greatly shorten their service life.

Lithium batteries do not need watering, which eliminates the problem of improper watering. Lithium batteries will not be damaged due to partial charging or insufficient charging, so this problem is also eliminated. If the lithium battery is seriously over-discharged or charged with a high current below the freezing temperature, it will damage the lithium battery and shorten its service life.

Heat also affects the battery. Higher temperatures will degrade the battery faster.

Because of these factors, coupled with different types of batteries have different service life, it is difficult to determine a specific time frame. Check the manufacturer’s battery specifications to understand the function of the battery.


Now you have some understanding of 120ah deep cycle battery. It is obvious why they are important for many different applications.

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