To charge a deep cycle battery, connect it to a 10- to 15-amp charger set to the appropriate current and voltage, based on the battery's specifications. Check electrolyte levels before charging, and be careful not to overcharge, as this can cause damage to the battery.
Before starting the battery charge, make sure that the electrolyte level within each cell is filled to approximately 1/8 inch below the split ring splash barrel. If levels are low, refilling with distilled or deionised water is preferable, but normal tap water is also acceptable.
To avoid overcharging the battery, check its instructions to determine the amount of charging time required. A charger with a timer reduces chances of overcharge.