How to Charge Deep-Cycle Marine Batteries

by Will Charpentier
A battery charger is one charging option.

A battery charger is one charging option.

A deep-cycle marine battery isn't used for starting your boat. It keeps the cabin lights burning and the stereo playing. Unlike the starting battery that's rated in cold cranking amps (CCA) and used for short bursts of energy to start your motor, deep-cycle batteries "are best at withstanding the deep discharges, recharging abuse and physical pounding of the marine environment," states Don Casey, an expert for the Boat Owners Association of the United States (BOATUS), in his library of boat manuals. Recharging these types of batteries is an uncomplicated process.

  1. Charge your battery from your boat's alternator. If your boat is wired for this, you'll have a battery selector switch on your dashboard. Setting the switch to the "Off" position will charge both your deep-cycle and starting batteries.

  2. Remove the battery from the boat if you and your boat are on shore, and connect the battery to a portable silicone-controlled rectifier charger. Attach the positive lead (red wire) from the charger to the positive post (marked "+") of the battery. Connect the negative (black wire) lead from the charger to the negative ("-") post of the battery. Set the charger's charge rate and voltage. The charge rate is the speed at which you want to charge the battery, listed as "Low," "Medium" or "High," and the voltage is listed on the battery. Plug the charger into a wall socket in your garage. The charger will shut down when charging is complete. You can also use this procedure while your boat is docked and you are "plugged in" to a dockside power outlet (called "shore power").

  3. Install a ferro-resonant charger on board and permanently connect it to your deep cycle battery. This procedure is recommended by boating experts like Don Casey, with the BOATUS, for, "live-aboards and larger boats with many 12-volt accessories."

    Permanently mount the charger on a level shelf (not above the battery). Connect a red battery cable from the positive post of the charger to a UL rated slow-blow in-line fuse, located within 18 inches of the battery, and a red battery cable from the fuse to the positive post of the battery. Connect a yellow (DC ground cable) from the charger to the negative post of the battery.

Items you will need

  • Alternator
  • Silicone-controlled rectifier battery charger
  • Ferro-resonant charger

About the Author

Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.

Photo Credits

  • battery charger image by Albert Lozano from Fotolia.com