Everything you need to know about Deep Cycle Batteries

Everything you need to know about Deep Cycle Batteries

by: Dean Janse Van Vuuren
July 2020
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Batteries are often divided into 2 broad categories, deep cycle batteries, and SLI (starting, lighting, and ignition) batteries. Most of us are familiar with SLI batteries as they are commonly used in cars and, as a result, are known as automotive batteries as well.

Deep cycle batteries remain a mystery to the wider audience. In fact, some people fail to make the distinction between deep cycle and SLI batteries.

To clarify any confusion, BPZ will address the topic of deep cycle batteries today.

We will highlight the properties of deep cycle batteries, that differentiates them from SLI batteries. We will then transition to the different types of deep cycle batteries and good practices for using deep cycle batteries.

Finally, we would conclude the topic by discussing different applications of deep cycle batteries.

Deep cycle batteries are designed to deliver a steady current over a longer duration of time. This sets them apart from SLI batteries which supply a currents load for a short duration of time. If we look at lead-acid variants of both battery types, we can get further clarity.

A deep cycle battery has thicker plates and a lower surface area than SLI batteries. However, it can sustain this lower magnitude of current for a longer duration and to deeper depths of discharge. Some high-quality deep cycles like the DISCOVER DRY CELL also incorporate great PSC (partial state of charge) features. This means that as in most cases where deep cycle batteries are not able to be fully charged every time when in use, less sulphation damage will result on the plates. On the other hand, SLI batteries have thinner plates which means more plates can be accommodated within the battery and increases the overall surface area. The higher surface area allows them to produce higher magnitudes of current for shorter time periods (i.e. lower cycle capabilities). Deep cycling SLI batteries will result in their early demise.

There are various battery types that have both SLI and deep cycle variants. Since our focus is deep cycle batteries, we would look at the types of batteries that fall under its umbrella. The most common types of deep cycle batteries are lead-acid batteries as they are less expensive and readily available.

A category of lead-acid battery is sealed or maintenance-free batteries. Sealed batteries are also referred to as VRLA (valve regulated lead acid). VRLA batteries have further sub-categories namely AGM (absorbed glass mat electrolyte) and GEL (gelled electrolyte) batteries.

Lithium ion batteries are considered as modern deep cycle batteries. Each of them comes with their own pros and cons with regards to their functionality and discharge and re-charge characteristics.

There are some good practices one should follow when taking care of lead acid deep cycle batteries. It is best to avoid discharging below 20% of their full charge capacity on are regular basis. It is permissible to discharge by 50% and or 80 % on an irregular basis. If the battery is not being used, recharge it to full capacity before storing it in a cold dry place to prevent any damage to the battery itself. Apart from that, a general checkup of battery voltage levels and fluid levels (if required) is recommended as well. During extended storage, a lead acid battery should not discharge below 12,2 volts. This is critical. During the discharge process (even self-discharge when not being used) sulphation occurs on the battery plates. Once the battery voltage drops below 12,2 volts the sulphation process could be such that the battery may NEVER be recovered to full capacity and as a direct consequence – a shorter life span. This is applicable to both deep cycle and SLI lead acid batteries.

Lithium Ion batteries may be stored in a partial state of discharge for longer periods of time and recharged to FULL capacity.

A WORD OF CAUTION - once a lithium ion battery has been discharged by 100% and then left in this state for a long period of time it may never have the ability to be recharged.

Some Advantages to Lithium Ion batteries:

98-100% Depth of discharge (DOD) with little or no damage. Batteries must however be recharged quickly after being discharged
Very quick re-charge times. If the batteries are rated at C1 or C.5 this effectively means for example that a 50 ampere hour battery, when charged with the correct 50 Amp charger, could be fully charged in one to one and a half hours.
Lithium ion batteries are very light in weight making them very easily managed especially when located in obscure places

Some Disadvantages to Lithium ion Batteries

They may not re-charge if the temperature is below zero degree Celsius.

They would have to be recharged in a “warmed environment “ above zero degrees.

Note: They can be effectively discharged however at zero degrees Celsius.

On the basis of the properties mentioned earlier, deep cycle batteries are ideal for various applications. They are used commonly in conjunction with solar panels and other off-grid energy solutions. They are also used to power electric vehicles like golf carts and forklifts as these vehicles do not need to accelerate to high speeds but move at steady speeds. They are most commonly used in leisure vehicles and off-road trailers. Deep cycle batteries are also used for marine applications such as house batteries in sail boats

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