[rescue] [Slightly OT] Smart-UPS 1400 Battery replacement

[BSD Bob the old greybeard BSD freak]

> > 1) disconnect all the wires from the batts.
> > 2) measure the voltage on each batt, they should all be within 1/4 volt of the
> > average of all their voltages (if not, deadsville).

Not necessarily.  Sometimes one or two cells will sulphate up in a 3 cell
battery (or a 6 cell battery), and when that happens the voltage on that
battery may be less than the  number of good cells x 2.0v/cell.
Sometimes the battery voltage will indicate good (e.g., 6v) but the
battery has lost sufficient internal water that it cannot conduct the
current.  The battery may look fine, but it is basically unusable in the
normal battery mode.  Both conditions can occur.

Also, a perfectly good battery may be discharged due to leakage currents
and look dead.  The only way to assess that is to run several cycles of
charge-discharge under load.  If it has not sat discharged for too long
(e.g., in surplus somewhere), it may be entirely resurrectable.

> > 3) if any batt is below .5 volt per cell, then the batts are gone. each cell is
> > good for 1.5v, so if its a 6v batt, then thats 5 cells.

Generally yes, but not always, per above.  If a battery has a voltage
of 1.0 volts per cell for a non-lead-acid battery, then that is probably
quite fine.  If a lead acid battery has less than 90% of its voltage
rating, across the entire set of cells in that battery (3 or 6 usually)
(at 2.0 volts per cell) then that could indicate one of more sulphated cells. 

> > 4) re-connect and charge for two days.
> > 5) place a dead load (resistive load, like a bunch of light bulbs) on the ups.
> > Pull the ups plug and see if the ups has decent output (measure it and watch
> > the bulbs). This is a cheatin way of measuring load capacity.

You need to do that across each battery.  I use a 6 or 12 v car headlamp
as the load.  Only one bad battery cell in one of the UPS batteries can
cause a UPS to go funny.  All the rest of the batteries may be entirely
fine.  BE HIGHLY SUSPECT of any batteries that have cells that are in
the least big swollen at the sides, as you sight along the side edge
of said battery.

> > 6) disconnect batts and measure for equality like in step 2.
> 
> once "charged" what identifies a bad battery?  Just being out-of-line
> with the others?

The battery should sustain its rated load current into a load for either
1 or 7 hours.  If the battery is a 7ah battery, it should deliver 1 amp
for 7 hours before reaching its low voltage value, or 7 amps for 1 hour.
If it cannot do that, then it is less than optimal.  It may still be
usable until way less than that, depending upon its actual current
usage cycles, but as to standard rating, if it is less than that,
then it is most likely going south for good.

The above all said, as relates to UPS or rated use.  When these things
do go mostly dead, I get years of light duty service out of them in
amateur radio power supplies, where only a few ma are needed, and
have some of them that are 20 years and more old.  It just depends
upon what you actually are doing with the critters.  UPS use tends
to overcharge the cells over time, boiling out their limited water
supply.  That is the pain you get for running so-called maintenance
free batteries or sealed batteries or gel-cells (actually 99.99% are
NOT gelled electrolyte cells but actually ARE sealed lead acid cells).
About 10 years back I wrote an article on these things and a search
for batterie.ps should turn it up.

Bob