How to Charge a Deep Cycle Marine Battery

••• battery charger image by Albert Lozano from

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Deep cycle marine batteries are a specialized type of power cell that is created to be able to run very low on power and not malfunction. In fact, if a deep cycle battery is used only slightly and then the charge topped if, this is the fastest way to ruin this type of battery. The term deep cycle means just that, they take a deep power cycle and run to nearly empty before needing to be charged and this is how they are intended to be used. Charging them is not difficult but needs to be done correctly.

Items you will need

  • Smart charger battery charging unit

Install your smart charger, 12-volt battery charging system. This charger is wired into your electrical system and attached permanently to the battery. It requires being plugged into a 120-volt service when the boat is connected to a land electrical line.

Remove and install a new deep cycle marine battery if replacing an old one. If you are having trouble holding a charge with your deep cycle battery, recharging it will not correct the problem. If the battery does not hold a charge it has outlived it's useful life and needs to be replaced. Connect a new battery to the positive (red) and negative (black) terminals with the battery cables. Attach the charger same color to same color.

Run the battery charger on your deep cycle battery according to the instructions of the unit you purchase. All permanent charging systems are designed to stay on the battery full time, and some monitor the battery for power levels and add charge when necessary.

Unplug the charging system from the electrical connection when not in port or connected to an electrical hook up.

Check the battery periodically with a battery tester or voltage meter to be sure it is maintaining a correct charge. Be sure to remember these batteries are designed to run down to a very low charge before recharging, and if this is not regularly done the battery will no longer take a full charge.