How to Test RV Deep Cycle Battery? Top 3 Methods are Well Explained

You don’t want to be stranded on the side of the road because your battery died. Nor do you want to risk a disaster because you tried to charge a dead battery. This means checking the RV battery’s capacity. We’ll discuss how to test RV deep cycle battery levels in detail for each method and how to stay safe while you do so.

If you don’t know how to test RV deep cycle battery, then read on. 

Here are the top 3 methods to test an RV battery

Method 01) Monitor Panel

This is the simplest method available, though it can be prone to errors since the user can make mistakes and the monitor panel doesn't always read right. It isn't uncommon for a battery level indicator to say 100% when it is rounding up from 80%.

The method itself is to look at the dashboard monitor panel while the recreational vehicle is not plugged into an electrical outlet. This will tell you the battery's current level.

Many people make a mistake of checking the panel while they're plugged into the grid or charging it from a generator (or the RV's motor). This gives them a false "charged' reading.

Disconnect the RV battery from any power source

Sometimes the battery monitor panel isn't accurate due to stored energy or reading fluctuations as the actual level. To ensure an accurate reading, while still disconnected from any power source, turn on a light and check the monitor again. 

If the level is close to where it was without this load, you know the monitor panel is accurate If the level is somewhat lower, use the lower value as the current indicator of the battery's level. And turn off all these loads once you have your answer so you don't drain the battery.

Method 02) Digital Voltmeter

If you have a sealed battery and don't trust the battery indicator light on the panel, you need to use a digital voltmeter to check the RV battery.

Before you do this, know what voltage the battery is After all, a 6 volt battery that reads 6 volts is fully charged whereas a 12 volt battery that reads at 6 volts is dangerously low. Avoid testing a battery that has been charged or discharged in the past six hours.

How to Test the Battery using a Digital Voltmeter

Find a voltmeter for this test and set it to DC voltage. If you have an electrical multimeter, you can use it as a voltmeter for this purpose after you set it to DCV, direct current voltage.

Make sure your test leads are properly plugged into the voltmeter. The red test lead should be plugged into the voltage (ohm) port while the black lead should be plugged into the "com" port.

Put the red lead on the positive terminal of the battery. Put the black test lead on the negative battery terminal. A digital voltmeter will give you the voltage in numbers. An analog voltage meter will point to the approximate value.

How to understand the Result? (Good or Bad)

A twelve volt battery should read between 125 and 12.7 volts. A reading of 12.66 means the battery is 100% charged. A six volt battery should read somewhere between 6.25 and 6.4 volts. If you get a lower reading, the battery needs to be charged.

For example, a reading of 11.9 volts on a 12 volt battery means it has totally dissipated. A reading of 12.06 volts means the battery is 25% charged, whereas you need 1245 volts or 75% to be able to start the engine most of the time.

If you get a generic error message, retest or replace the batteries in your voltmeter before taking another reading. If charging the battery doesn't improve the voltage levels, the RV battery itself probably needs to be replaced.

Method 03) Hydrometer/Specific Gravity

The hydrometer technique tests the specific gravity of a battery's electrolyte; in short, a hydrometer test is a specific gravity test of your battery. You can find both manual hydrometers and digital hydrometers for this test.

Note that you can't get an accurate reading via this method if you just added water to the battery; let it sit for at least six hours before you check the battery with the hydrometer technique.

This method is an option if you aren't sure how to check the battery level with a voltmeter or just don't have one A benefit of this approach is price — you can find hydrometers for a couple of dollars and get it at almost any auto parts store.

How to check RV battery using Hydrometer?

The hydrometer is dipped into the sample. You give it enough time to reach equilibrium (this is the equilibriation time). The level of equilibriation gives you the density of the material on a calibrated scale. 

This test method requires you to put on protective gear and open up the battery. This isn't possible if you have a sealed maintenance-free battery. Nor should it be done while the battery is hot, since you don't want acid-laced steam escaping from the battery and hitting you in the face.

Suppose to understand Easily

Suppose the battery is cool and you're wearing the proper safety gear. The electrolyte will typically be in two different levels, an upper level and a lower level.

Fill the hydrometer and drain it twice before you take a reading. This helps clear out any moisture or residue in the hydrometer that count the results. Now test the specific gravity of the electrolyte in one cell. 

If you're using American units, 1.225 to 1.250 is suitable, and anything heavier is ideal. Anything lighter than this indicates a problem. Once you have the reading, drain the electrolyte into the cell it came from. Then repeat the process on the other cell.

The Final Step of your hydrometer test

After you test all the cells and record the values, replace the vent covers. If the readings of all the cells averages to less than 1277, the battery needs to be charged. If the readings between cells has a difference of more than 0.050 (between the highest and lowest), the lowest cell is either weak or dead. This suggests the battery needs to be replaced.

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John S.

Hello guys! I'm a 37-years-old author, traveler, writer, blogger, and a camper. I enjoy life as much as I can and love to visit beautiful places in my RV. That's why while traveling I have decided to dedicate some time to share my experiences with everyone that might be interested in traveling, camping, and RVs.