Maintaining and Testing my RV Batteries

Our RV Batteries

All the batteries in our rig are of the lead-acid (wet cell) variety. There are other types commonly used in RV nowadays such as Gel Cell, AGM (Absorbed Glass Mat) and even Lithium Ion. This article will only deal with my lead acid type which are generally cheaper but require a little more on the maintenance side of things.

My Keystone Cougar fifth wheel trailer came new from the dealer with a single 12-volt deep cycle type battery. Because we enjoying spending time off the grid I installed an additional pair of higher capacity 6-volt golf cart batteries to use when boondocking. Also, our big Ford diesel truck is equipped with a pair of large 12-volt automotive starting batteries.

Love Your RV! | Boondocking

That’s 5 lead acid batteries in total to keep maintained and operating in tip-top condition. It doesn’t take too much neglect to seriously lower your batteries performance. Things like corroded terminals and low fluid levels can have a dramatic effect. Luckily maintenance is very simple, you just need to take a few precautions because are dealing with very corrosive sulfuric acid.

Maintaining my RV Batteries

Every month or two there are several checks I perform on all my batteries.

Is the battery casing bulged, discolored or cracked?

The first thing to check is the physical appearance. If I see any cracking or bulging out of the plastic casing I would be replacing the battery. Likely something is internally wrong with it and it definitely is not worth having it leak in your engine compartment or RV storage bay.

Are the terminal connectors tight and clean of any corrosion?

If not I will remove the wiring and clean the battery posts and wire connector lugs. Wire brushes work well for this as well as a mixture of baking soda and water. There are also many commercial terminal battery cleaners and sprays on the market.

Baking soda and dieletric grease

To prevent future corrosion, you can coat the exposed metal positive/negative connector surfaces with a thin layer dielectric grease. A fellow RVer friend of mine highly recommends a product called Fluid Film. Most auto stores will have something similar or in the past I have even used good old Vaseline. Anything that is not conductive and stops air and moisture from reaching the metal should work.

Does the battery have proper fluid levels?

This maintenance is the most often overlooked and causes many of the failures in RV lead-acid batteries. Over time, a battery can lose fluid through outgassing. On the battery top, you’ll find removable caps allowing you to check the battery fluid and top up with distilled water. The fluid level must always remain above the lead plates inside the battery to prevent damage.

Battery Caps

It takes a little peeking down the holes with a flashlight to see the lead plates. The proper level on most battery brands is about a 1/8 of an inch before plastic fill hole wall starts. Usually an inch or so from the battery top. This gives room for expansion without overflowing.

For topping up the batteries, you must use mineral-free distilled type water only. I like to use a turkey baster instead of a funnel to aid in filling. The baster allows me to be very precise in how much water I add. If during filling or testing my batteries I accidentally splash any of the battery fluids  I use the baking soda/water mix with a paper towel to neutralize it. Then wipe away the excess liquid.

Filling the Battery Cell with Distilled Water

Testing My RV Batteries

I test my RV Batteries in two ways. One with a digital voltmeter and two with what is called a hydrometer.

The state of charge of a lead-acid battery can be estimated from the density of the sulfuric acid solution used as electrolyte. A hydrometer calibrated to read specific gravity relative to water at 60 degrees Fahrenheit is a standard tool for servicing automobile batteries. Tables are used to correct the reading to the standard temperature.

Prepping the Batteries for Test

Before performing the voltage and hydrometer tests the batteries need to be fully charged, then disconnected and let sit for at least several hours. Then connected to a load and run for a few minutes to remove any surface charge. I usually just run my trailer water pump or turn on my truck lights. Once these steps are taken the battery is ready for an accurate test.

Voltage Test

This test is very easy, just place the leads on the positive and negative terminals and have the multimeter set to DC volts. Based on the reading you can determine the state of charge. A fully charged 12-volt battery will read around 12.6 – 12.8 volts, half that for a 6-volt battery.

Hydrometer Battery Test

This test is also very simple but a bit messy and can be dangerous because you are dealing with the highly corrosive battery fluids. You first carefully remove the battery filler caps trying not splash any of the battery fluid around. Then dip the hydrometer in sucking up a test sample. I usually do it a few times to get an accurate reading. The hydrometer will measure the specific gravity of the battery fluid to determine if the mix of sulfuric acid and water is right.

Measuring the Specific Gravity

Battery Charge Voltage Specs

The hydrometer will have a series of lines and numbered/colored graphs showing the charge level. The beauty of the hydrometer is you get to test individual cells versus the voltage test that only tests the overall battery. I believe it is a more accurate way of testing the battery.

Tips for Working with Lead-Acid Batteries


  • Wear disposable rubber gloves to protect your skin from the corrosive acid.
  • Remove jewelry and wear old clothes.
  • Have some sort of type of eye protection – battery acid in the eye sucks big time, mmkay.
  • Mop up any splashed acid with paper towels and dispose of them in a plastic bag.
  • To neutralize battery acid spills use a mixture of baking soda and water.
  • Have a fresh water source handy in case you need to quickly flush acid from skin or eyes.

Video Showing Me Testing My RV Batteries

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