How to change and charge your boat’s battery
Changing and handling a battery should be done carefully and thoughtfully. Did you know that a charging battery gives off hydrogen gas? Mix hydrogen gas with a little air, add a spark, and you have the perfect recipe for a disaster. Let’s lay out some ground rules.
Rule no. 1: No smoking around a charging battery.
Rule no. 2: Have a well-ventilated area for charging.
Rule no. 3: Do not charge batteries while they are connected to a wiring harness.
When disconnecting a battery from the wiring harness, remove the wires from the negative terminal first and then remove the wires from the positive terminal. By removing the negative first, you will avoid a spark, which could occur if you do it wrong. When reconnecting a battery, attach the positive first and then the negative for the same reason.
If you have safely disconnected the battery, you can remove it from its box or safety frame.
Next, use a hydrometer to decide if the battery needs charging. A hydrometer is a glass vial with a calibrated weight inside. When fluid is drawn into the vial, the weight floats. The height at which the vial floats depends on the specific gravity of the liquid drawn into it. If the specific gravity is below 1.225, the battery needs to be charged. If it reads above 1.265, it does not need charging.
Next, look for consistency in the battery’s cells. No two cells should have specific gravities that vary more than 10 percent.
If you need to charge the battery, first determine the rate of charge. The rate of charge for deep cycle batteries is 20 percent of the battery’s ampere-hour rating. Hook up the battery to the charger (positive terminal first, then the negative). Don’t use a high ampere automotive-type quick charger, or you will overheat and destroy your expensive marine battery. Periodically shut off the charger and check the specific gravity of each cell to make sure it’s charging.
Remember that battery acid is corrosive. Don’t get it on your skin, clothes or in your eyes. Wear protective gloves, long sleeves and safety goggles.