Tags
marine electronics boating

The batteries used in boats today are high-tech and expensive. The operator should be able to measure the charge and translate the reading into the condition of the battery. Here are a few methods for measuring the charge of a marine battery.

There are measuring tools available for purchase that can be used to measure the state of charge of a battery if you do not have a voltage metering system installed. For batteries that use electrolyte there is something called a Hydrometer, which can detect the amount of sulfuric acid in the electrolyte and displays this reading as a charge. The amount of sulfuric acid will change with temperature so in order to ensure consistent readings, be sure the battery is around 80F. Additionally, electrolyte batteries will have multiple cells so the hydrometer readings should be taken from each individual cell. Use the owner’s manual of your hydrometer to determine if the reading is good or bad. A bad battery will typically have deviations between cells. A good battery will have consistent readings between cells.

At your local hardware store you can purchase a very convenient tool that all boat owners should have called a Voltmeter. A handheld voltmeter will have two leads, typically red and black. The red is positive and the black is negative. If measuring the charge of a marine battery, you are measuring DC voltage. DC voltage is indicated (in most cases) by a straight line with three dots above it. (Alternative current or AC is a wavy sinusoidal line). Turn your selector switch to DC and place the black lead on the negative battery terminal and place the red lead on the positive terminal. A fully charged battery will indicate on the low end 12.6 volts and on the high end 13.2 volts on the read out. A dead battery will read about 10.5 volts. We recommend using a digital volt meter as the reading is more accurate than an analog. NOTE: in order to get the most accurate reading using a voltmeter, we suggest keeping the battery in a steady state for 24 hours.

If you have a pricey battery system installed on your boat, it may be worth installing a meter that monitors amp-hours. This is the best way to get the most accurate reading of a battery that is in use. It will give the rate and the time of the current flowing out from or in to the battery to give you an idea of how much useful life you have left or how long you have until it is fully charged. If you do have this system installed in your marine electrical system, we highly recommend you become intimately familiar with the owner’s manual.