Boating 101 – On-board battery charging

On-board battery charging means you have at least one battery on board.

On-board battery charging means you have at least one battery on board. Batteries, like everything else on board, require maintenance, but they are one piece of gear that may not be as well understood as some others.

Batteries on boats tend to be lead-acid batteries, so that’s what we mean when we say battery. These batteries employ a sulfuric acid electrolyte and can generally be charged and discharged many times if you follow a few rules and pay attention to the manufacturer’s instructions. Keeping the electrolyte level in the recommended range is necessary.

There are three battery technologies:

  1. Wet or Flooded Cell: Still the most cost effective.
  2. AGM (Absorbed Glass Mat): Uses a fiberglass separator to hold the electrolyte in place.
  3. Gel: The electrolyte is thickened with an additive to keep it in place.

And each of these is available in two types.

  1. Cranking: Short duration, heavy loads (engine cranking, bow thrusters)
  2. Deep Cycle: Longer duration, lighter loads (trolling motors, lights, radios, inverters)

Generally, all batteries should be recharged immediately after use. When you crank an engine, the alternator begins charging as soon as the engine turns. Lead-acid batteries will experience substantially longer life when a multi-stage charger is used to float charge the battery. This prevents the battery from ever being low between uses. Proper temperaturecompensated float voltage chargers will yield the best results.

Opportunity charging is the process of charging a battery whenever power is available or between partial discharges rather than waiting for the battery to be completely discharged. Trolling motor batteries with a charging circuit (from the main engines) will benefit while running from spot to spot. By avoiding complete discharge of the battery, the number of times you cycle it can be increased.

Some Common Myths About Batteries

  • A battery will be discharged by letting it sit directly on the floor. Not true. But when batteries were made of glass and wood and low resistance materials, a battery could conduct to a damp concrete floor and slowly discharge—but no longer.
  • Running your boat will fully recharge the battery. Unless driving a multi-stage external regulator, an alternator is not a battery charger; it’s a battery maintainer. It is true that a lightly discharged battery may regain full charge under normal use, but a severely discharged battery must be recharged by an auxiliary (on-board) battery charger. Further, deeply discharged battery banks, once the engine is started, can put an enormous load on the charging system. Running the boat will put charge in the battery, but the only way to make sure is to use a multi-stage charger.
  • Lead-acid batteries have memories. Lead-acid batteries do not have a memory. However, continuous undercharging will lower the capacity of the battery over time. Deep discharges left unresolved can damage batteries and will shorten their service lives.
  • Sealed Gel and AGM batteries are dangerous. Gel and AGM batteries are much safer than non-sealed wet cell storage batteries. When installed and maintained in accordance with the manufacturer’s instructions, they significantly minimize the chance of acid spray, fumes and explosion hazards. Their completely sealed design also eliminates acid spills, corrosion and gas emissions, making them safer for use around you and your gear.

Pick your battery type and technology based on your wallet and needs. Keep the electrolyte level full and make sure to maintain the charge as often as possible. Finally, consider an on-board charger. When you consider the expense of new batteries, a charging system on a small boat makes sense. It’s convenient, good for the gear and helps makes sure the boat is ready to go when you are. As an owner, if you find something suspect consult an ABYC-certified technician.

For specific questions, email or call (888) JOE-ZINC.