In Clare Snyder writes:

UPS'es will often not charge the battery at all if the voltage
has dropped below (something like) 8V.
It's not a problem with taking a charge - it's a problem with
supporting the load. A GOOD UPS does a self-check every once in a
while - and if the battery does not meet spec it alarms.

I've picked up units that had been pulled out of service,
unplugged from the outlet, but with the batteries still
connected... and put into a closet for the summer (we're
talking schools), which became a couple of years.

I've sold (and serviced) hundreds of UPS units from cheap 250 va
standby units to very expensive 3KVA online units for over 25 years.
ANd I have yet to run across a UPS that would not attempt to charge a
dead battery.

We're bumping into different companies and models. I've certainly
had a few.

Virtually no battery charger with reverse connection protection will
charge a dead battery. I have often used my lab power supply to
"kickstart" dead batteries.

I've got alligator clips on a bnch
of dumb wall warts...


[a] by "work" I mean get a modest amount of run time from them.
Don't count on full cycling...

Don't count on them supporting hald the rated load either.

I've used a bunch of these to keep cable modem and tv
tuner boxen working for those half second glitches
when the electrical utility switches loads on and
off twenty miles away...


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