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.

The 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 www.usbattery.com.

10 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?

    Reply
    • 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?

      Reply
  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.

    Reply
    • Mike Wallace
      Mike Wallace says:

      Hi Karen,

      The most likely reason is due to charging. Gassing/bubbling is normal during the end phase of charging as the voltage is at the highest point. The gassing/bubbling mixes the electrolyte to ensure it is homogeneous throughout the battery. If the battery is bubbling when charging hasn’t recently occurred then it could be a short in one of the cells. It would be really obvious since the bubbling would be in only one of the cells. 99% of the time the bubbling is happening for the right reason.

      Reply
      • Wes
        Wes says:

        Hey there, I have 6 12v batteries I fill 3 sections each with water.. running in parallel.

        I’m in the north where we have far below freezing temps all winter. Do I need to remove the water completely from each section for the winter? Will u still be able to use to batteries for lights in the cabin over the winter? Cheers!

        Reply
        • Mike Wallace
          Mike Wallace says:

          Hi Wes,

          Make sure to top off all 6 cells of each battery to the proper fill line using only distilled water. Our engineers do not recommend that you remove the electrolyte during the winter. However, they do recommend limiting your depth of discharge based on your ambient temperature. Using the freezing point chart below and your average ambient temperature, determine your state of charge lower limit. If you discharge your battery below that state of charge, you risk freezing your batteries. Frozen batteries are typically permanently damaged.

          Best,
          -Mike Wallace, Creative Manager
          Freezing-Point-FLA

          Reply
  3. Noah
    Noah says:

    Hey, I got a brand new 12v pre charged battery for my quad and it didnt work, I tried charging it and still nothing. I took it apart and found that there was barely any water. I filled it up and charged and it held a voltage. But, when I put it in my quad it didnt turn over and smoke came out of my battery. Any idea on how and why this happened?

    Reply
    • Mike Wallace
      Mike Wallace says:

      Hello Noah,

      Thank you for choosing US Battery for your quad! We’re sorry to hear about your premature battery failure.
      Our engineers need some additional information to accurately diagnose your situation:
      1. Battery model
      2. Date code

    • a. Flooded lead acid – date code is stamped directly into the positive terminal. Two letters and a number.
    • b. AGM(yellow case) – date code is laser etched somewhere on the cover.
    • 3. Voltage before trying to turn it over.
      4. If your battery is a flooded lead acid, please provide the specific gravities of each cell. You can use an EZRED battery hydrometer they are cheap and easy to use.

    • a. AGMs cannot be checked for specific gravity.
    • Please send this information to our Product Engineer Matthew Ealy mealy@usbattery.com

      Best,
      -Mike Wallace, Creative Manager

      Reply

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