Know Your Battery’s Water-Fill Level

Anyone who has a set of deep-cycle flooded lead-acid batteries knows that proper maintenance includes checking the water level in each cell, after a full charge. Although it’s easy to carefully add water to each cell, many people get confused as to how much water to add. Too little, and they’ll be having to add more sooner than is necessary. Too much and it runs the risk of overflowing when the batteries are charging.

care-maintenanceThe proper method recommended by most battery manufacturers is to add enough water so that the cell plates are completely submerged, but not so much that the water is up to the battery case cell cap vents. The proper fill level, according to battery manufacturers, is approximately 1/4-inch below the fill well bottom. (See photo example)

Battery manufacturers also recommend using only distilled or deionized water and to use a watering gun or pitcher to fill each battery cell. Ensuring your batteries are properly watered will add life and provide optimum performance from your deep-cycle batteries. For more information on battery maintenance, visit

4 replies
  1. Bobby Ratliff
    Bobby Ratliff says:

    I have two Interstate deep cycle rv batteries 3 yrs old. Notice they don’t hold a good charge lately. I keep the battery save switch off when not in use. I’ve been confused about the water level and after reading your post I realized I was filling too much water (almost io to the top) Could this be the issue?

    • Mike Wallace
      Mike Wallace says:

      Hi Bobby, Adding too much water shouldn’t cause an issue unless over-filling is causing the cells to overflow. Any significant overflow could cause loss of acid and this would impact the batteries’ ability to hold a charge. If you have a hydrometer, you should check the specific gravity after charging to make sure they are charging fully. Our engineers were wondering how long do the batteries generally go between uses, and what kind of charger are you using?

  2. Allan
    Allan says:

    I’ve had my two US Battery six-volt batteries (US 145XC) for almost seven years now and have maintained the water levels on them yearly and put a maintenance charger on them during winter. They have served me well. MUST check the levels, and only use distilled water.


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