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Vol 49 | Num 4 | May 22, 2024

Offshore Report Ocean City Report Delaware Report Virginia Report Snarky Lines Ship to Shore The Galley Issue Photos
Ship to Shore

Article by Capt. Steve Katz


What is 12.6? That is the voltage of a fully charged standard lead acid (traditional, sealed or AGM) marine battery at rest. If you have a 24-volt system, then 25.2v represents a fully charged 24v bank. If your battery is reading 12.0 volts at rest, it is 50% discharged! If a battery remains discharged, sulfation can occur.

Sulfation is a buildup of lead sulfate crystals and is the number one cause of early battery failure in lead-acid batteries. Sulfation occurs when a battery is deprived of a full charge, lead sulfate crystals build up and remain on battery plates. When too much sulfation occurs, it can impede the chemical to electrical conversion.

Sulfation can be avoided by properly charging and re-charging your battery.

What’s that smell?

When your engine is running or your battery charger is on, the battery voltage should be between 13.7 volts-14.7 volts. If your battery area smells like rotten eggs, then you have a battery problem. Batteries contain an electrolyte comprised of water and sulfuric acid. When overheated, the sulfuric acid is converted into a gas called Hydrogen Sulfide and it is this gas that smells like rotten eggs. Over-charging a lead acid battery can also produce hydrogen sulfide gas. The gas is colorless, poisonous, and flammable. If you smell this odor on-board your boat, turn off the charger, vent the area and stay away until the odor disappears.

Most marine batteries last 3 to 5 years, depending on how they are cared for and how many discharge and recharge cycles they have been through. There are some technical differences between standard lead acid batteries (traditional, sealed or AGM) marine batteries and the popular AGM style batteries, though a little bit more expensive, are very resilient to charging and discharging and have become the high-performance standard for marine batteries.


If your only source of power to recharge your battery is the alternator on the boat’s engine, it is a good idea to confirm your alternator(s) are working properly. Alternators produce electricity measured in volts and amps. Most alternators produce about 14 V of DC power and the amperage varies depending on the size of the engine/alternator combination. Minimally, a small outboard alternator may produce around 30 A and upwards to over 100 A on a large diesel engine.

Voltages are easy to measure and confirm since the volt reading is easily available on the engine gauge or other gauges on board the boat.
The alternator(s) amperage is more difficult to measure and often, an amperage gauge is not included in a standard package. The voltage should be consistent, and the amperage will vary depending on the load. Once the batteries are charged, and the electrical loads are reduced, the amperage will automatically lower to a minimum amount.

If you do not have an amp gauge, there is no need to worry since the volt gauge can still give you the relative health of the electrical system. If the voltage is consistent and steady, your alternator is most likely working properly and producing the correct number of amps.

Though, if you notice your voltage dropping during a boat trip, it would be a prudent idea to investigate the cause, because today’s modern engines rely on good electrical power.

If your boat has an onboard battery charger, the battery charger will maintain and top off the batteries to keep them full, with or without the engine alternator operating. A modern battery charger will slow the charge down as batteries become full and maintain their charge by using a small amount of voltage and current called a float charge. A charger without this feature could overcharge the batteries and permanently damage them.

Checking the health of your batteries and maintaining them throughout the season will help provide a reliable season of battery power. §

Coastal Fisherman Merch
CF Merch



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