Boat Battery Tech Tips

POINTS TO REMEMBER
The battery is the heart of the electrical system. Always start troubleshooting at the battery. Never store a battery in a discharged state. Never add anything except distilled water to a battery.

IMPORTANT BATTERY FACTS
A good battery can provide four or five years of worry-free service with the right kind of care. Bigger is better! The battery you are replacing does not have to be the same size as the original. It is always better to have extra battery capacity.

DRY CHARGED BATTERIES MUST BE CHARGED BEFORE USING
Many small batteries are supplied with the electrolyte in a separate container. If you have to fill a new battery with electrolyte, you must place the battery on a quick charger. The charging system will never bring the battery to a fully charged state. The battery capacity will never be above 80%. Pulling the battery out later and trying to charge it will not work. The battery’s capacity has been permanently cut by 20% and there is nothing you can do about it.

BATTERIES WILL SELF DISCHARGE WHEN STORED
Batteries will self discharge when stored for long periods of time. This is a normal process with all lead acid batteries. Always charge the battery to full charge before storing. Also disconnect the negative battery able. This will keep the small system drains from accelerating the discharge process. The best way to avoid hortened battery life is use a SMART CHARGER (not a trickle charger) that will maintain the battery at a full state of charge by only charging the battery when the voltage drops to a specified level without overcharging.

ELECTROLYTE BECOMES WATER IN A DISCHARGED BATTERY
As a battery becomes discharged the percentage of sulfuric acid in the electrolyte becomes less. The sulfuric acid combines with the lead plates producing lead sulfate. As this happens the electrolyte solution becomes pure water. A discharged battery will freeze in cold climates, which will destroy the insulators and plates inside it.

LOOSE BATTERY TERMINAL ENDS CAN DESTROY A BATTERY
Loose or corroded battery cable lugs can cause all sorts of problems. When the starter is engaged the loose or corroded connection can cause a heavy arc which will melt the post right out of the battery. If the battery is gassing, the arc can cause the battery to explode. Never use the temporary type battery ends. These are only good for emergency use and will become corroded in a short period of time. Always use a crimped and
sealed battery cable end or replace the battery cable.

BATTERY TESTING PROCEDURES

WARNING! Batteries give off hydrogen gas constantly. Hydrogen gas is highly explosive. Always wear safety glasses or goggles and use caution when working with batteries.

OPEN CIRCUIT VOLTAGE TEST
Before you can properly test any battery it must be at FULL CHARGE. You can verify the state of charge with the use of a digital multimeter. Connect the digital multimeter to the battery terminals. A fully charged 12 volt battery will read at least 12.6 volts (2.1 volts per cell) on the multimeter. If your reading is 12.4 OR BELOW you must recharge the battery before testing.

Open Circuit Volts / Percent of Charge
11.7 volts or less / 0%
12.0 / 25%
12.2 / 50%
12.4 / 75%
12.6 or more / 100%

LOAD TESTING THE BATTERY
Before you can properly test any battery it must be at FULL CHARGE.
The only way you can thoroughly test a battery is to place a high amperage load across the battery terminals.

Starter motors have very high amperage requirements which can exceed 300 amps on certain engine applications. If the battery has to be recharged you must first remove the surface charge. This can be done by using the starter. Disable the ignition spark (consult manufacturer’s method to avoid electronic ignition) and crank the engine for 10-15 seconds. Once you have removed the surface charge, disconnect the battery cables and connect the battery load tester to the battery posts.

Determine the cold cranking amperage rating of the battery you are testing. If the cold cranking amp rating (CCA) is not known, use 450 CCA for four cylinder engines, 550 CCA for six cylinder engines and 650 CCA for V-8 engines.

Adjust current draw on the load tester to 50% of the CCA rating. Continue this for 15 seconds while viewing the voltage reading on the battery tester. The voltage should stay above the specified reading (see chart below) without falling off. If the voltage remains at the specified level or above, the battery would be considered good. If the voltage reading drops below the specified level, replace the battery.

Load Test Chart
Minimum Voltage / Temperature
9.6 / 70 F 21C and above
9.5 / 60F 16C
9.4 / 50F 10C
9.3 / 40F -1C
9.1 / 30F -7C
8.9 / 20F -12C
8.7 / 10F -18C
8.5 / 0F -18C

This information is from the ARCO Starting and Charging Catalog which can be found on this website.



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