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I have a Zoeller sump pump with a deep cycle battery. How long do these deep cycle marine batteries last and need to be replaced?

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  • Most batteries have a three to five year expected life. Some might last longer, but that is considered bonus/lucky time. This is for most brands of batteries.
    – crip659
    Commented May 9, 2022 at 14:35
  • Is this a recognised brand or a cheap one?
    – Solar Mike
    Commented May 9, 2022 at 14:52
  • This really comes down to opinion or when it quits charging. On my generators at work I have to change the batteries every 3 years huge ones same on the back ups for the fire alarm (many different sizes smaller) the brand is not specified so the AHJ knows they will last for 3 years, my boat I usually get 5-6 years on them. It all comes down to how often it is heavily discharged each severe cycle shortens the life and battery manufacturers actually have life curves based on depth of discharge cycles.
    – Ed Beal
    Commented May 9, 2022 at 19:53

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The useful life of a deep cycle marine battery depends on how often and how deeply it is discharged and the quality of the charger. If a deep cycle battery is properly charged and rarely discharged it can easily last 6-8 years. If deeply discharged often, it can go bad in 2 years or less.

Rather than replacing the battery on a schedule, buy a battery load tester and test the battery every six months. An inexpensive load tester -- half the cost of a new battery -- puts a load of 100 amps on the battery and displays voltage during the test. If the voltage drops below a certain level during the test, the battery should be replaced. Just follow the instructions that come with the load tester.

In the long run the small investment in a load tester will save money by allowing you to get the maximum useful life out of your batteries, and it will prevent you from relying on a battery that is already past its useful life.

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  • Thanks. Bought a load tester. It says it is good/ 60% on the CCA test. It is a FVP Voltedge battery. Is there a magic # where it is better to change it or just wait for the tester to say it is bad?
    – shikarishambu
    Commented May 26, 2023 at 21:16
  • @shikarishambu There's no magic number. It depends on the application and the potential for economic loss if the battery doesn't perform. In my best Clint Eastwood voice, I'd say, "You've got to ask yourself, do you feel lucky?" In other words, is 60% of original capacity enough for your sump pump to sail through the longest expected power outage during the worst expected high water table event? Only you can answer that question based on past experience and your crystal ball.
    – MTA
    Commented May 26, 2023 at 21:50

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