The battery fluid on my sump pump Marine Deep Cycle Battery dried up to be completely gone.

I've replaced it with distilled water. Will the trickle charger bring it back to life, or am I in the market for a new battery?

UPDATE: the battery did not come back to life. Given that I didn't want to fuss with adding water in the future, I purchased an AGM battery from the company that makes the pump. It was comparable in price to AGMs at the local auto parts store.


2 Answers 2


How did the electrolyte boil off in the first place?

The typical reason is a very cheap battery charger that did not know how to charge the battery properly. Modern state-of-the-art battery chargers can charge lead-acid without any boil-off at all.

You hear about "maintenance-free batteries" for cars? That's a lie, the battery depends totally on the alternator being modern/sophisticated and knowing how not to overcharge the battery. If you use a maintenance-free or SLA battery on a garbage charger it will boil off electrolyte anyway, destroying the battery since there's no way to refill it.

The old way, back when battery chargers and alternator regulators had no silicon and were all relays that went clack-clack... you did boil off some, and you regularly replaced it with distilled water. That was part of the routine maintenance a garage would do when they changed your oil. Nobody does that anymore.

So whatever charger did this damage is a piece of junk. Note that a great many "12V sump pumps" are el-cheapo models mainly designed to trade money for peace-of-mind, rather than actually being reliable units that will last.

You can try refilling and recharging this battery. I would use a regular battery charger like one intended for an automobile battery.


Assuming you want your sump pump to work in a power outage, new battery.

If you have a different, deader, battery to trade in when you do that, feel free to hack about with this one, for some non-critical use, but the odds of it getting back to full capacity from that sort of abuse are nil.

  • 3
    Separately, OP should do a test every 2(?) months to make sure the system works as expected. Just like testing smoke detectors, for peace of mind.
    – Criggie
    Commented Aug 3, 2023 at 11:24

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