Perce

Living on a boat, I deal with deep cycle batteries continually.

EVERYTHING ABOARD runs off of my batteries and I take good care of them
since I hate cold beer. (yes 12vdc refrigeration)

The uncovered plates will have begun to oxidize as soon as exposed to
air. The liklihood of being able to recover from that depends on how
long they were uncovered. By the way, a "fully charged" 12vdc battery,
when not connected to any load at all, and not charging, will read 12.6
volts. So reading higher as you stated is a positive indicator.

When batteries are charged they are (or should be) put through three
stages of charge:

Bulk charge - where the battery accepts about 80~90% of it's capacity to
charge. A lot of current can be put into the batteries through this
charge. When bulk charging I see 50 amps or more.

Absorbtion charge - topping up the battery until the voltage reaches
around 14.1 volts. The amount of current put into the batteries tapers
off during this charge as the voltage increases.

Float charge - once FULL absorbtion voltage (14.1) is reached, the
charger should drop the voltage back to around 13.25 or there abouts,
and current is minimal (a couple of amps tops). That's the charge the
keeps the battery topped up.

The LED on the charger may be nothing more than a volt meter reading.
There is no way to know what your charger is doing without the specs.
Most lower cost chargers don't really do much but shut off at a pre-set
voltage. Perhaps the LED indicates that the charger is off, and you can
measure with a volt meter to see what point the charger shuts off and
deteremine how it handles charging. Refer to the voltages above to see
when it shuts off and that will give you a rough idea of what the
charger does.

As for your battery and it's possible damage:

There are a few things that you can do. First, as already suggested, top
up all cells and watch them as you charge the battery. If one cell tends
to loose electrolyte much more quickly than the others, the cell is bad
and the battery is toast. In simple terms (it's a bit more complicated
than this) a cell that is bad will be shorted, and the short causes it
to get hot, and that boils off the electrolyte. Similary, if one cell
seems quite hot compared to others, the battery is toast.

Pick up a hydrometer and check all cells with it after charging and
letting it rest with no load for 15 minutes. Any LARGE differences after
charging indicate that the battery is toast. If a cell reads partially
charged and all others read charged, the cell is in trouble.

If charging for a period of time (overnight) doesn't bring the battery
up to an even charge on all cells (as measured with the hydrometer)
after 15 minutes no charge, no load, then there is one last ditch effort
you can take.

You can equalize the battery. Basically the battery is significantly
overcharged in an effort to redistribute the electrolyte and force the
sulphur on the plates (called sulfation) back into the electrolyte.

Typically, the voltage applied is about 16vdc, and the equalize is done
over about 8 hours. The battery will bubble like mad so remove the caps
to allow it to vent. It will give off explosive hydrogen gas, so no open
flames...take all precautions to prevent explosion. And it will loose
electrolyte so you'll need to top it up during the process. Since it is
a high voltage charge, turn off or disconnect all loads. In my case I
turn off all breakers, fridge, stereo, instruments, Han radio,
everything that is powered is disconnected to prevent damage.

If after a full equalize the battery cells differ substantially when
measured with a hydrometer, the battery is history.

I hope this helps.

Bill


Percival P. Cassidy wrote:
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?

Perce
(This is my usenet alias. I *am* an FCC-licensed "ham," but my real name
and callsign have no relevance to this question.)