How to Charge a Boat Battery

How to Charge a Boat Battery

Keeping your boat’s battery charged is crucial for a smooth day out on the water. A dead battery can leave you stranded, ruining your fishing or boating trip. This guide will teach you everything you need to know about charging a marine battery correctly and safely.

How to Charge a Boat Battery (Step by Step Guide)

Follow these steps to properly charge your boat’s battery:

  1. Turn off main battery switch if equipped.
  2. Disconnect battery cables, negative first.
  3. Clean battery terminals if dirty.
  4. Connect charger leads to battery posts – red to positive, black to negative.
  5. Plug in battery charger and turn on.
  6. Allow battery to charge fully, checking progress periodically.
  7. Once fully charged, turn off and unplug charger.
  8. Disconnect charger leads, black first.
  9. Reconnect battery cables, positive first.
  10. Turn on main battery switch. The battery is now ready to go!

Using a Portable Charger on the Water

You can bring a portable battery charger like a NOCO Genius onboard to charge your battery while on the water. Simply connect the leads temporarily to give your battery a quick boost until you can fully charge it back on shore power.

How Long Does It Take to Charge a Boat Battery?

The time it takes to fully charge a boat battery depends on several factors:

  • Battery size – Larger batteries take longer to charge. For example, a large 150Ah deep cycle battery could take 12 hours or more to fully charge.
  • Battery type – Standard flooded lead-acid batteries charge slower than AGM or gel batteries. Lithium batteries can charge very rapidly with the right charger.
  • Charger amperage – Using a charger with higher amperage will charge a battery faster. A 10 amp charger charges quicker than a 2 amp “trickle” charger.
  • Depth of discharge – If the battery is deeply discharged it will take longer to recharge than if it has only been shallowly discharged.

On average, you can expect a fully discharged small to medium sized lead-acid boat battery to take 8-12 hours to charge. Larger or heavily used batteries may need even longer.

Boat Battery Charging Times

This table gives an estimate of charging times based on battery capacity and charger amperage:

Battery Size2A Charger10A Charger
35Ah7 hours1.5 hours
70Ah14 hours3 hours
105Ah21 hours6 hours
140Ah28 hours8 hours

As you can see, having a 10 amp or higher output charger can significantly reduce charge times, especially for larger batteries.

How Often Should You Charge a Marine Battery?

  • Actively used boat batteries should be charged after each use, especially if they were deeply discharged.
  • Batteries on boats in seasonal use should be charged at least monthly to maintain them during storage.
  • You should also charge the battery before the first trip of the season.
  • For maximum battery life, don’t let the charge drop below 50% if possible. Recharge after each use.

Tips for Charging Boat Batteries

Follow these tips to safely charge your marine battery:

  • Use a battery charger designed for marine/deep cycle batteries. Automotive chargers can damage a boat battery.
  • Be sure to use the correct voltage – 12V for a 12V battery system.
  • Disconnect the battery cables before charging.
  • Connect the charger leads properly – red to positive, black to negative.
  • Charge in a well-ventilated area to dissipate hydrogen gas produced.
  • Don’t leave batteries charging unattended for long periods.
  • Make sure terminals are clean before charging for proper contact.


Charging your marine battery properly and regularly will keep you on the water instead of stranded with a dead battery. Follow these charging guidelines to extend your battery’s life and your boating enjoyment.

You might also be interested in reading:

Steve Momot

Steve Momot

Steve is an accomplished professional photographer and marketer who specializes in the Fishing, Yacht, and Boating industry. With a strong presence as an influencer and marketing expert in the Marine Industry, he has made a significant impact in the field. Additionally, Steve is the original creator and co-founder of Sportfishtrader. Prior to his career as a marine photographer, he gained extensive experience as a licensed boat and car dealer in South Florida.

Leave a Reply

Your email address will not be published. Required fields are marked *