How to Charge a 12-Volt Deep Cycle Battery

There are three basic types of deep cycle batteries: standard wet cell, absorbed glass mat and gel cell. The batteries are rated by the amount of times they're fully charged and discharged. In most all cases, the average rating is approximately 300 cycles. Cycles are the number of times the battery moves from full discharge to full charge. Many deep cycle batteries are sealed, so no monitoring of the fluid level is possible. All deep cycle batteries require the use of an electronic charger. The electronic charger monitors the voltage and current fed to the battery.

Things You'll Need

  • Safety glasses

  • Steel brush

  • Electronic deep cycle battery charger for your particular type of battery

  • Distilled water

Step 1

Wear safety glasses during the removal, cleaning and charging process.

Step 2

Remove the battery from the equipment it's servicing. If equipment is connected to the battery, the charger will give false readings while applying power, and will damage the equipment, the battery and the charger.

Step 3

Place the battery on a firm surface in a well-ventilated area. During the charging process the battery emits hydrogen gas that's highly explosive.

Step 4

Clean the battery's lead posts with the steel brush. Remove all foreign accumulation from the battery connections. The result must be a shiny metallic color to the lead terminals.

Step 5

Open the top caps of the wet cell-type deep cycle battery, if applicable. Not all wet cells will have access to the internal battery cells. Check the fluid level. If the level is above the internal battery plates, don't add water. If the plates are exposed, add enough water to cover them.

Step 6

Use only the deep cycle battery charger manufactured for your type of battery. Read the top labeling on the battery for the proper type. Wet cell deep cycle battery chargers cannot be used with the absorbed glass mat or gel cell types. Consult the manufacturer's specifications.

Step 7

Attach the red charger connector to the positive (+) terminal on the battery. Secure the black charger connector to the battery's negative (-) terminal. Plug the charger into the wall outlet.

Step 8

Observe the two lights on the face of the charger. The red LED light indicates that charging is taking place. The green LED light indicates that power is present from the wall outlet. If either of these lights is blinking, there is a problem. Consult the battery charger manufacturer's instructions to identify the problem. Each manufacturer uses a different code to the blinking lights for diagnosing problems.

Step 9

Unplug the charger from the wall outlet after the red light has gone out. Remove all connections from the charger.

Step 10

Check the internal fluid level for the wet cell deep cycle battery. Top it off with distilled water. The final fluid level must be just below the internal plastic ring in each cell opening. Replace the battery into the device or equipment.


Keep all sparks and open flames away from the charging battery, or an explosion can occur.

Thoroughly wash your hands and remove clothing if you happen to the spill liquid contents on yourself while transporting the battery.

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