On Jan 2, 11:40*am, (Dave Platt) wrote:
In article ,
Andrew Rossmann wrote:

I have a battery I bought for an APC UPS about 4 years ago. I bought 2,
and used one immediately. I kept the other on the side as I have several
UPS's that use basically the same battery. Of course, over time, it has
discharged itself. I measured about 4.3V instead of the normal 12-13V. I
put it in a spare UPS, which immedialy complains if I try to turn it on.
Luckily, the UPS charges even when it is off, but slowly. I measured
about 15mA initially, and after about 36 hours, about 7.5mA. It is
currently up to about 10.7V.

How much damage do you think was done to the battery? I know it will
lose some capacity.

It sounds as if the battery has become badly sulphated. *This is not
uncommon if you let a lead-acid battery sit around un-used... the
lead plates have become coated with a layer of lead sulphate, in a
crystalline form which is both insulating, and difficult to convert
back to a soluble form. *The battery now looks pretty much like an
open circuit to the UPS, as it has a very high resistance, and it will
not accept a charge efficiently from the recharging circuit.

To keep this from happening (in the future) it's best to keep the
battery fully charged, via a "float-charge" mechanism at just the
right voltage (which depends somewhat on the temperature).

There are techniques which can be used to de-sulphate a battery and
restore it to at least some degree of usefulness. *The techniques
vary in detail, but usually involve applying a higher voltage to the
battery (with a careful limit on the amount of current available!) to
break down the sulphate crystals and allow them to re-dissolve. *This
is sometimes done via a "pulser" (which generates short high-voltage
pulses) and sometimes through a dedicated high-voltage supply.

Whether a badly sulphated battery can ever be returned to a
substantial fraction of its original capacity seems to be a somewhat
controversial question... some say yes, some say no. *It may depend a
lot on the specifics of the battery type and the degree of sulphation.

Your best bet is probably to just buy a fresh battery, when you know
you need it for one of your USP systems... and check the date code on
the new battery before you buy it to make sure it's really fresh and
hasn't been sitting on a shelf for several years!

--
Dave Platt * * * * * * * * * * * * * * * * * AE6EO
Friends of Jade Warrior home page: *http://www.radagast.org/jade-warrior
* I do _not_ wish to receive unsolicited commercial email, and I will
* * *boycott any company which has the gall to send me such ads!

Usually you need to buy the battery a couple of days BEFORE you
discover you need it :-)

At work we had a very large UPS that used 600V of gel-cell 12V
batteries each about the size of a largish car battery. In the 15
years or so that it was in use, there were, perhaps, 5 power failures
and the UPS failed every time even though all the routine maintenance
and testing was observed. Other than the first time when it was only a
month or so old and the inverter blew up [linerally] all the rest of
the failures were due to battery failure.

Neil S.