Whenever your RV sits in storage the battery(s) lose its charge over time; not to mention the parasitic loads that can drain batteries in storage. I recommend testing the battery state-of-charge monthly and charge any battery that is at or below an 80% state of charge. But just how do we accomplish this? Let’s look at my top 7 tips for testing your battery state of charge.

Note: An 80% state of charge for a 12-volt battery is 12.5 volts. An 80% state of charge for a 6-volt battery is 6.25 volts.

There are basically three (simple) ways to test the condition of your RV batteries.

1. You can use the monitor panel in the RV.
2. You can measure the voltage with a digital voltmeter.
3. You can test the specific gravity with a hydrometer.

• The least accurate of the three methods is using the RV monitor panel, but if this is your only means for checking the battery(s) it will give you a general idea of the condition. When you check the condition of your battery using the monitor panel make sure the RV is not plugged in to shore power, if it is you will get a false fully charged reading. To get a more accurate reading of the battery’s condition check the monitor panel when the RV is not plugged in and turn a couple of overhead lights on to place a small load on the battery.

• Measuring voltage with a voltmeter has its advantages. If you have sealed (maintenance free) batteries your only choice is to use a voltmeter; and measuring voltage can give you a quick picture of the batteries depth of discharge so you know when they need to be recharged. To measure the voltage, you need a good digital voltmeter. Set the meter on DC voltage and connect the red lead to the positive terminal and the black lead to the negative terminal.  A 12-volt battery that is fully charged should read 12.6 to 12.7 volts. Readings below 12.6-volts indicate the battery state of charge is less than 80% and the battery needs to be charged.  A 6-volt battery that is charged should read 6.37 volts. Readings below 6.25 indicate the battery state of charge is less than 80% and the battery needs to be charged.

RV 101 Tip: To get an accurate reading the battery should not be tested if it was charged or discharged in the last 12 hours and preferably 24 hours.

• The preferred method for testing the battery’s state-of-charge is to check the specific gravity reading of each cell. You can purchase an inexpensive hydrometer at an auto parts store for about ten dollars. Electrolyte is a solution of acid and water, so you need to wear safety glasses and gloves and avoid any contact with your skin or clothing. Remove the vent caps and check the electrolyte levels. There must be enough in the cells for the hydrometer to pick up a sample. If you need to add any water, you’ll have to charge the battery and let it sit for 12 hours before testing. Fill and drain the hydrometer at least twice in each cell before taking a sample. Take the reading and record it then drain it back into the cell. Test all the cells and replace the vent caps. Specific gravity readings for a charged battery should read between 1.235 and 1.277. Specific gravity readings below 1.235 indicate the battery state-of-charge is less than 80% and the battery needs to be charged.  If there is a .050 or more difference in the specific gravity reading between the highest and lowest cell, you have a weak or dead cell in the battery.

• If you put your RV in long term storage, it’s a good idea to remove the batteries and put them in storage too. This is quite simple to do. When you remove a battery always remember to remove the negative terminal first and then the positive terminal. Label the battery cables or take a picture so you remember how to make the connections next spring. Clean the batteries with a 50/50 mixture of baking soda and water if necessary. Check the electrolyte level and add distilled water if necessary. 

• Regardless of whether the batteries are left in the RV or removed you should test the battery state of charge monthly and charge any batteries that are at or below 80%. A discharged or partially charged battery will freeze much faster than a charged battery. Store the batteries in a cool dry place but not where they could freeze.

RV 101 Pro Tip:

With all of that said, let me tell you what I do with all my batteries. I use a product called Battery Minder. It not only charges the battery, but it is also a conditioner and maintainer. The two most common causes for RV battery failure are undercharging and overcharging.  Undercharging is a result of batteries being repeatedly discharged and not fully recharged between cycles. If a battery is not recharged sulfate material attaches to the discharged portions of the plates and begins to harden into crystals. Eventually this sulfate cannot be converted back into active plate material and the battery is ruined. This also occurs when a battery remains discharged for an extended period. Sulfation is the number one cause of battery failure. The second leading cause of battery failure is overcharging. Overcharging batteries results in severe water loss and plate corrosion. The good news is both problems are avoidable. I personally use a product called the Battery Minder to maintain my batteries when the RV is in storage. The Battery Minder monitors the batteries and supplies the amount of current needed to keep them at full charge. It also dissolves the harmful sulfate material, and it will never overcharge the battery regardless of how long it is connected. So it charges, maintains and conditions your batteries all in one.

Important Note: When selecting a Battery Minder product make sure it is designed for use with the type battery you have. Battery Minder does offer products for lithium batteries too.

Happy Camping

Mark J. Polk

RV Online Training