How to Charge a Deep Cycle Battery Properly?

These batteries are used when there is a need for a battery to provide a steady voltage for long hours. Deep cycle batteries are used, for example, in a boat to provide power for the installed lights and the equipment for longer hours without going off or without turning dim even when the charge is almost flat. These batteries should always offer high amp levels for a short period to restart the engine over again.

Deep cycle batteries are made differently in such that the method of charging is also different compared to charging other types of batteries. This creates a great difference between handling deep cycle batteries and burst batteries. This article contains steps and guidelines on handling deep cycle batteries and how to charge them appropriately.

Charging a deep cycle battery appropriatelyCharge A Deep Cycle Battery

You need to first know the correct charger for your battery. Different types of chargers include; flooded chargers, AGM chargers, and GEL chargers. When a battery is charged using the correct type of charger, its battery life will be improved, but when a wrong charger is used, it may damage the battery. You should always note that high amps highly damage AGM and the GEL type of batteries.

The main difference between charging the flooded batteries and the GEL and AGM type of batteries is that flooded batteries take a longer period before fully charging, while the other two types take a short period.

How to use deep cycle battery chargersHow to use deep cycle battery chargers

Most current battery chargers have specific settings for both the GEL and the AGM type of chargers. Always ensure you use this setting when charging your battery, as it will help in increasing the battery’s life. If a charger is only designed for the AGM type of battery, it usually has two main differences compared to other chargers.

These chargers regulate the charging rate by making sure your battery charges up to 100 percent without overcharging. Once they are fully charged, the system will block the charge from overcharging your battery.  A high percentage of AGM batteries will undergo three stages. These stages are;

  1. a) The bulk charge stage – a very low amp charge is used at this level to avoid overcharging the battery. It is usually the main charging cycle of all.
  2. b) The absorption charge stage is usually the second. This stage is achieved when the battery gets to 80 percent. At this stage, the current is reduced until it gets to 100 percent. Charging continues gradually until full.
  3. c) The float charge stage is the last one. The charge is just maintained at 100 percent at this stage.

How to use a regular chargerHow to use a regular charger

This charger will use a high amp to charge your battery for a short time. Flooded batteries can be used using this type of charger, and they cannot get damaged. The AGM and GEL batteries should not be charged using the regular chargers as a fast charge easily destroys them. The high charge rate of regular chargers causes heat production in the battery, preventing batteries from fully charging.

Regular batteries are somehow disadvantageous as once the charge is complete, their systems do not stop the charging. Hence, they are prone to overcharging, and you need to be cautious to switch off the power once the charging is complete.

ü Every battery charger should supply around 10 percent of the maximum amperes produced by your battery.

Estimated hours to charge your batteryEstimated hours to charge your battery

The best thing is to have smart battery chargers, which automatically choose the best charge rate of your battery. Once the battery is fully charged, it immediately turns to maintenance mode. If you do not have this kind of charger, then the only option is to operate manually. You should divide the outputs of the battery rating to estimate how long you need to charge your battery.

In such circumstances, it is advised to charge your battery at low amp rates. In other ways, this can be calculated by using a charging calculator.

Steps on how to directly charge your batterySteps on how to directly charge your battery

Step 1; ensure that the terminals of your battery are clean. You ensure this by cleaning all the dirt particles and grease around the terminals. In case of rust, a ball of wire wool is recommended.

Step 2; tightly connect the wires to the battery terminals. Ensure there are no loose wires.

Step 3; you now need to connect the positive cable labeled red to the red terminal. When this is tightly done, connect the negative cable colored black to the negative terminal.

Step 4; connect the charger to the switch and switch the power on. If charging has started, most batteries will notify you. When charging is complete, a smart charger will also notify you. When using a non-smart charger, switch the power off when the time you calculated is over.

Precautions when disconnecting your charger and battery

Plug off the charger and then disconnect the negative connections first. Remove the negative cable followed by the positive connections. Then grease the terminals. Greasing terminals prevent them from corrosion.

How to charge a deep cycle battery using an alternator as the second batteryHow to charge a deep cycle battery using an alternator as the second battery

It is not recommendable to charge these kinds of batteries in parallel forms. The alternative methods to use are listed below;

  1. By use of an isolator. An isolator’s purpose is to allow batteries to charge separately. It charges the batteries at a low voltage until the batteries are equal, and then it will charge the batteries simultaneously.
  2. By using a special tool, for example, the pro mariner mobile charger. It is usually connected between the batteries and the alternator. When using this tool, the alternator is forced to produce maximum output, reducing the charging times of the battery.

Troubleshooting deep cycle batteries that won’t chargeTroubleshooting deep cycle batteries that won’t charge

First, try charging another battery with the same charger to know which of the two has a problem. When you are done, you need to check whether the charger you have is the best for your battery. Depending on the type of battery you have, you can know what charger to use. If this still is not the problem, check whether the battery is sulfated. If this is the case, you need to replace your battery.

In other circumstances, it could be that the battery is just too old to function any longer. It would help if you again replaced it with no hesitation.


You should always ensure that the charger you are using fits your battery well. If the charger is not right for your battery, the battery’s life span will be reduced, and still, it can get damaged in that it does not store charge for long hours as it normally should. Unless circumstances force, do not undercharge your battery. Undercharging will also destroy the working life of your battery.

In circumstances where you’re unable to tell whether the battery is damaged and the above steps do not help you get your answer, you need to test the battery by use of a multimeter. When you measure the battery’s voltage, you can tell whether the battery is damaged or not. If you cannot read the voltage or operate the multimeter, contact a professional to help you out and avoid causing other damages to your battery and your charger.

In this video, I show you how to maintain and charge your Marine, RV battery.

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