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How to Test Your RV Battery

Clint

Test the charge of your RV’s battery to know when it needs to be charged or when it needs to be replaced.  There are a few different ways to test the charge.  You can use your RV’s monitor, check the voltage with a voltmeter, or test the specific gravity of the electrolyte solution inside your battery’s cells with a hydrometer.  Here are some details on each of the options.

RV dashboard

Dashboard Monitor

The easiest way to test your battery’s charge is by looking at your RV’s dashboard monitor if your unit is equipped with one.  First make sure your RV is unplugged or you will get a false reading.  Then simply check your battery’s charge.  Also try turning on a couple of lights to put a small load on the battery and check the charge again.

Voltmeter

Voltmeter

Another method of checking the charge in your battery is by using a voltmeter.  Obtain a voltmeter and switch it to dc voltage. Then make sure that nothing in the RV is turned on and that the battery is not being used.  You also want to make sure you know what voltage your battery is; most are 12 but 6 volt batteries are also used.   To test the battery’s charge, put the voltmeter’s red lead on the positive battery terminal and its black lead on the negative battery terminal.  Often times the terminals are marked with the same colors.  A 12 volt battery should be somewhere between 12.7 and 12.5 volts and a 6 volt battery should be somewhere between 6.4 and 6.2 volts.  If your battery is any lower than those ranges, then you need to charge it.  Also if your battery’s charge appears to deplete quickly you should probably replace it.

Hydrometer diagram

Hydrometer

Finding the specific gravity of the cells in the battery is probably the best way to test the charge.  It is also easier to tell if you need to replace the battery using this method.  First you will need a hydrometer which is basically a device used for measuring the density of liquids.  You can usually find them at auto parts for ten dollars plus or minus a few dollars.  Be sure to get one that compensates for temperature.  You will also need some gloves and safety glasses because you will be dealing with an acidic solution.  Once you are ready to test your battery, remove the vent caps and check the electrolyte level in each cell.  There has to be enough of the solution to make the hydrometer float.  If there is not enough you can add some water, but you will then have to charge the battery and wait around six hours before you can test it.   When you are ready, fill the hydrometer with the electrolyte solution and drain it back into its cell at least twice before taking your reading.  If you are unsure of how to use a hydrometer, click here.  This site talks about hydrometer use with brewing beer, but it is the same principle.  Test each cell and write down the results.  The specific gravity of each cell should be between 1.277 and 1.235.  If all the cells average below that, then your battery needs charging.  Take note if there is a difference of .05 or more between the highest and lowest cells.  This could mean that you have a bad cell and may need to replace the battery.

So now you know how to test your battery.  Hope this little article helps you out.

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