Guide to Charge Your Deep Cycle Marine Battery

The modern boat relies on electrical power from onboard batteries for nearly all of its essential functions. When used in marine or automotive applications, the voltage of a deep-cycle battery sometimes drops to the point where your boat or its electronics no longer function.

That’s why you need to have a dedicated charger to keep your battery at the recommended voltage. Charging a marine battery is relatively quick and unproblematic.

Poor battery performance is often the unfortunate result of incorrect battery charging techniques that severely limit our successes and memories on the water. Incorrect charging of a high-quality marine battery can also become a hazard in a short period of time. To avoid such misfortunes, it is quite simple to learn how to properly use and charge deep cycle marine batteries.

Cleaning the terminals

Cleaning the battery terminals is not strictly necessary if there is no rust/corrosion, so you can just skip this section. However, if it is necessary, get appropriate tools/materials to avoid accidents. Use rubber gloves and safety glasses for your protection and paper towels, a wire brush and sandpaper to remove the acid deposits.

When we say corrosion, we are referring to a white and powdery substance that looks like it can be blown away by the wind. This cleaning will remove the deposits along with any poor connection between the lead wire and the battery. A poor connection will only increase charging times with less available battery power.

Start by wearing latex gloves and safety glasses for protection and wipe away excess corrosion with the wire brush. You will need sodium bicarbonate/baking soda solvent, spray it on the badly corroded areas. Now dilute 1 tablespoon of sodium bicarbonate in 1 cup of water in this solution. Wipe off the excess and thoroughly clean any residual rust/corrosion from the terminals with sandpaper.

Choosing the Right Charger

In general, the battery terminals should be cleaned before starting any charging process. And when it comes to charging, using a proper charger is the practical requirement for any type of battery, not just a marine battery.

So before you connect the positive and negative cables in a methodical arrangement to the positive and negative terminals, you should look for the right type of charger. Buying the wrong type of charger will definitely be a big waste as it will not only not provide enough power for a full charge, but will also promptly damage your battery.

A deep cycle battery charger that reaches full capacity above all else will provide the right amperage as well as voltage for the marine battery in a timely manner. Smart chargers are considered the best chargers when it comes to marine dual purpose batteries – starting and deep cycle.

These chargers are also known as multi-stage chargers as the charging process involves 3 phases. Smart chargers have the technology to charge your marine battery followed by its temperature and chemical structure.

The connection of the charger to the battery

The charging process can only start when there is no corrosion. First, connect the terminals of the marine battery to the charger of the right type. After all, if you connect a stupid charger to the battery, only increases the risk of permanent damage to the battery, which will affect its service life.

Here, a smart charter delivers power in 3 phases which includes the bulk phase before the decrease phase and finally the float phase. When plugged in, it maximizes the charge while preventing damage to the battery’s internal components.

If you do not already have a smart charger, quality marine smart battery chargers cost around $50 to $100 and we recommend them as they will extend the life of your marine battery.

Charging the battery

We will assume here that you have found the right type of charger, so now connect the battery terminals to the charger terminals. Once connected, switch on the battery charger and the charging process should begin.

The charger will take over the entire process at this stage, setting the charge first via the bulk method and then the accept method before moving on to the float phases. With an intelligent charger, the percentage state of charge of the battery is shown on the display LED.

However, if your charger is equipped with adjustable charge settings, it is imperative to read the manual before charging – both for the charger and for the marine battery charging technique. Reading and understanding the manual will help you set the best speed for effective charging.

A tip: A smart charger takes preventative measures against the risk of battery damage that can result from overcharging.

Removing the charger

Slide the charger to the off position when you have a fully charged battery. Next, you will need to disconnect the charging clips that you attached to the battery terminals. The process is complete when you reattach the cable to cover the battery box before returning it to the boat and enjoying its services. If you have another marine battery on board, you can repeat the whole process to get a full charge.

Battery Charging Cycles

Regardless of the design that a typical marine deep cycle battery has, it only allows a significant depth of discharge. You can only use up a fraction of the actual capacity of the marine battery by consuming it over many cycles before recharging it to full capacity over its lifetime.

A normal cycle that a deep cycle battery is designed for will certainly start at full capacity (100%), which will drain the battery by about (20-50) % of actual capacity before recharging to 100%. Battery life is also strongly influenced by the overall depth of discharge.

A battery that frequently has a depth of discharge of 50% is expected to last longer than a battery that is allowed a greater depth of discharge. Repeated shallow discharges down to 5-10% contribute to shortening the life at the same time. From a pragmatic point of view, high-quality deep-cycle batteries discharge as they are designed to do before being recharged to full capacity.

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