I have a 115AH deep-cycle battery that I bought as a stand-by battery for
my amateur radio station. It has been in a "battery box" on trickle-charge
(using a charger with a "deep-cycle" setting) for most of the time since I
bought it over a year ago, and it has been called on to supply power only a
few times.

Recently I noticed that the "fully charged" LED on the charger was not on
and started investigating further.

Having not encountered any batteries in the last few decades that have not
been sealed and "maintenance free," I was surprised to find tiny print
about checking the electrolyte level every 30 days -- but even then it
took me a few minutes to figure out how to get access to the cells to
check this.

Anyway, when I removed the cunningly disguised covers, I found that the
cells looked totally dry, and each took close to a pint of distilled water
to bring the electrolyte level above the plates.

The battery has now been on charge for about 20 hours at the charger's 12A
setting, but most of the time the ammeter on the charger has shown only
about 5A. The cells are all still gassing.

Is this battery likely to come back to life again, or is it toast? Any
remedial actions to take?

The battery may be recoverable, but I suspect it's going to take some
effort, and it may well have passed the point of no return.

The fact that the cells are drawing low current, but are
electrolyzing, suggests to me that you've got a combination of a high
charge voltage (above 14.4) and some pretty badly sulphated plates.
The bottom parts of the plates (where there was still some
electrolyte) may be OK, while the upper portions may be sulphated
and/or the separators may be clogged with solids.

First thing I'd do, is just give it some time on the current setting,
checking the electrolyte level periodically and refilling as
necessary. Given some time, the relatively high voltage may clear out
some of the sulphation and residue.

If not, then it might be worth trying to recondition the battery.
There are electrical desulphators available, which hit the battery
with a high-voltage high-frequency pulse in order to break up and
redissolve the sulphate crystals - some people say these work very
well, others are less impressed. I've also seen chemical desulphation
suggested, via the addition of some sort of chelation chemical (I
*think* EDTA is used but don't trust that possibility without
confirming it!).

If some of the plate material has disintegrated and fallen to the
bottom of the cell, then the battery is probably a goner. The residue
can end up shorting the cell.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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