battery power loss mystery

[d.]

I have a 6v NAPA commercial battery which I have maintained on a 6v maintainer charger...the battery is on the bench.
It has read 6.7v. for months; suddenly yesterday it read 4.3v.
I unhooked it and let it sit a day and repowered it...still reading at 4.3v.
What is going on ?
Did the battery just drop a cell overnight?
How would that happen?
all suggestions welcome.
thank you.

[Bill G]

Maybe the charger is at fault or the connection to the battery. I would check those first. Also, check the electrolyte in the battery cells.

[Patrick L.]

What does 'repowered it' mean ? If it means you recharged it, did the charger show full charge ? When on the charger does one cell bubble more than the others. It may be time to take a hydrometer reading. Have you checked to see if something is drawing down the battery ?

[DHZIEMAN]

No mention of the age of the battery. It appears you have one cell not taking a charge or ???? Your voltage is down just about one Cells worth. Older batteries due tend to fail!

[Standing Elk]

I just had to replace my battery for that same reason.

[jrelliott]

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You have a shorted cell in the battery. Time to get another battery. What happens is either there is a piece of one of the plates touching the other plate or the plates have warped coming in contact with the two plates in the battery. This condition can happen if you run the battery out of water, charge or discharge the battery at a high rate.

[d.]

Patrick, "repowered" means I re-plugged the charger into the wall after disconnecting it for a day.
The battery is on the bench, so no draw down, cells are full and always have been, connections are clean, no sudden discharge.
It just seems weird that overnight it went from 6.7v to 4.3v just sitting on my workbench.

[Patrick L.]

OK, I didn't know the battery was sitting on the bench. I'd still check each cell with a hydrometer, but, it seems like a cell is bad and the battery is now defective.

[eagle]

First off, try another charger for a few hours. If voltage comes back up, then there's a possibility it may still be ok. Chances are though, it likely needing replacement. Some maintainers run too high of a float but yours seems fine at 6.7V. I have had maintainers catch fire. However, I do run trickle chargers on batteries that sit unused a lot, although I hook them up for about 6 hours every few months, then disconnect them.

[chap52]

Use to be able to take batteries to an auto parts store and have them "load test" them for free. However many stores have gone digital and their fancy tool won't read a 6 volt battery. Hydrometer's are still available, even at Walmart or Amazon. Chap


https://www.walmart.com/search/?cat_...ery+hydrometer

[Mulletwagon]

The low cost hydrometer test is the way to go. Suspect one cell will show less floating balls than the rest which will indicate a bad cell.