On Sun, 2 Jan 2011 10:01:46 -0600, 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.

A charged but unused SLA should retain its charge for months. The
battery powered cars the grandkids love (got them on freecycle, not
new at $300 each) have 12 volt 10AH SLA batteries and typically get
charged twice a year (when the grandkids are here). I use a Black &
Decker charger that does 1 or2 amp charging (switch selected) and the
1 amp charge works well. The B&D charger is "smarter" than the
original charger which comes with a "do not charge more than X hours"
warning. Many UPS chargers are in the same category - they do a fast
charge to quickly replenish the battery after use, but there is no
"smart" monitoring. I've seen several different brands of small UPS
(300 watts or so) kill batteries in a year or less - even if unused.
The charging circuit simply cooks the battery.

Forget about using a UPS to charge a battery. Instead, buy a real
charger which won't destroy a bettery even if it's left on charge all
the time. For most UPS batteries, I would recommend the Black &
Decker Smart Battery Maintainer. It uses a switch mode power supply
and has LEDs for "charging" and "charge complete". The charger is $22
at amazon.com
http://www.amazon.com/Black-Decker-B.../dp/B000AMOEPA
and I've seen it for about $20 at Target and Walmart. If you can find
the older version with the 1amp/2amp charge level switch, it's even
better on the smaller batteries.

Keep an SLA battery properly charged and it will last a very long
time. The electric cars are typically driven until they no longer
move, so the batteries get a full discharge at relatively high current
(5 amps on level driveway; 15 amps uphill - more if two kids in one
car). These batteries have been in service two years and seem to have
close to their original capacity.

John