RV 101® Checking & Adding Water to an RV Battery

How much water should I add to my RV battery?

That’s a good question, but before I answer your question let’s talk briefly about checking the electrolyte levels in your lead-acid batteries. Checking the water level in lead-acid battery cells on a regular basis can save and extend the life of your RV batteries. The more a battery is used and/or charged the more water evaporates from the cells. I recommend checking the water level monthly and after each RV trip. If you leave the RV plugged in, constantly charging the battery, you should check the water levels bi-monthly.

Next it’s important to know you only add water to a fully charged battery, unless the water level is already below the plates in the cell. If the water level is below the plates add just enough water to cover the plates and recharge the battery. When a battery is fully charged the water level is at the most accurate level. This is when you should check battery water levels.

Note: If you are not comfortable working on or near lead-acid batteries have a qualified RV repair facility perform the battery maintenance for you. When you work around batteries wear goggles and gloves, remove all jewelry and do not smoke or use any open flames.

To answer your question when you add water to a battery you only fill the cell to 1/8 inch below the bottom of the fill-well or split-ring. If you look inside the battery cell you will see a plastic ring that extends down inside the cell roughly 1 inch. This is what is referred to as the fill-well or split-ring. The electrolyte solution in lead-acid batteries is a mixture of sulfuric acid and water. If you add too much water a couple things will happen that can be detrimental to the battery and to you.

  1. Adding too much water can deplete the required electrolyte solution of acid and water resulting in compromised battery performance.
  2. Adding too much water will result in corrosion caused by overflow during charging. Sulfuric acid is extremely corrosive and can can ruin paint, burn your skin and damage clothing.

Over filling a battery is bad, but it is worse when a battery is under-watered. When a battery is not recharged in a timely manner or when the plates are not covered by the electrolyte solution the plates begin to sulfate. The sulfate material attaches to the discharged or exposed portions of the plates and begins to harden into crystals. Eventually the sulfate material cannot be converted back into active plate material and the battery is ruined.  Battery sulfation is the number one cause of battery failure. Always make sure the plates are covered by the electrolyte solution. When you add water to a battery only use mineral free water, distilled water is best.

Follow these basic battery maintenance procedures and add years of life to your lead acid RV and automobile batteries.

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Happy RV Learning,
Mark Polk

RV Education 101

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4 thoughts on “RV 101® Checking & Adding Water to an RV Battery

    1. I don’t know why the generator stopped running without being able to see it. It sound like you have a Safe T Alert dual LP gas and CO detector. The first thing I would do is get the auxiliary batteries fully charged and then see what the detector does. They are sensitive to low voltage and that might be the reason for the flashing lights. These detectors are usually good for 5 or 6 years and they have the expiration date posted on the detector. If, after the batteries are charged the detector still flashes red and green it is most likely defective.


  1. Had my 2015 Fleetwood Bounder motor running about 10 days ago. Got in it today and the coach batteries were dead and the engine battery was dead (not a single noise when trying to start). I purchased a new engine battery and after installation, the engine started with no problem. After a minute, I started the generator and had it running so that it would charge the coach batteries. After a couple of minutes, the generator stopped and now it does not start. I checked and have 3/4 tank of gas. There is also a loud beeping noise coming from a “Safe T Alert” box down by the floor that is flashing 2 red lights and 2 green lights. On the outside cover plate it reads that when the lights are flashing that the unit is at “end of life”. Do you have any recommendations???


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