How to Replace a Boat Battery

by Tonya Yirka

Many boat enthusiasts replace their boat batteries about every two years if they do not recharge them regularly. However, avid sport boaters tend to replace theirs about every six months to a year to avoid electrical problems. Since the truly reliable batteries are expensive, many boat builders do not include them in new boats, so if having a battery installed by a qualified installer is out of the question or if the job is for a smaller vessel, some basic instructions can make the job easier.

Removing the Old Battery

  1. Purchase a deep-cycle battery that is compatible with the other batteries in the battery bank if applicable. This type of battery, says David Pascoe of Boat Battery Basics, tolerates a discharge up to 80 percent whereas other marine batteries only tolerate up to 50 percent, and it has a four- to six-year warranty. Also, be sure that the amperage is greater than that required to start the boat.

  2. Mix a solution of 50 percent water to 50 percent baking soda and keep it handy for neutralizing acid spills.

  3. Disconnect the earth connector from the black earth terminal ,which is the negative 5/16 inch, 18 threaded negative post of the old battery. This eliminates any shorting, boat damage or igniting of lingering oil vapors or fumes.

  4. Undo the red connector that is attached to the 3/8 inch,16 threaded red positive post of the battery.

  5. Lift the old battery out of the battery box.

Installing the New Battery

  1. Brush and clean the old cable connectors using a wire brush.

  2. Coat terminals and connectors with white grease to prevent corrosion.

  3. Connect the red positive connector to the red positive post.

  4. Connect the black earth connector to the black post.

  5. Charge the new battery with a charger that is made for recharging deep-cycle batteries.

Items you will need

  • Deep-cycle battery
  • Solution of 50 percent water and 50 per cent baking soda
  • Wire brush
  • White grease
  • Deep-cycle battery charger


  • Never install a new deep-cycle battery with other deep-cycle batteries that are over six months old. Do not hook it up backwards. Keep the battery switch off during the charge. Never lay anything on the battery that might connect the posts. Don’t tip the battery on its side. Secure the battery down. Encase the battery in a rugged, covered plastic battery box to avoid sulfuric acid leaks. Don’t let acid get on clothing. Don’t overfill a battery. Never charge a frozen battery. Don’t overfill a vent-well in the battery. Never use tap or well water to fill the wells in a battery, as they contain iron or salts, and chlorine, which can ruin the battery.

About the Author

Tonya Yirka is an Indiana-based writer who has focused on writing for online publications since 2009. She contributes many articles about Chinese culture and traditions to various websites. Yirka, a retired teacher, has a Bachelor of Science in education from Indiana University and attended classes toward a Master of Science in educational studies.