Thanks for all who replied. I looked up the pricing on
replacement batteries and found them kinda high for the
capacity I'd get. Obviously, if I install external batteries,
they'll be installed in a way that even if they leak, they
can't cause much damage (crawl space ;-) . I'll also put
in a fan that will turn ON if it the UPS is running on battery
power, or charging the batteries.

BTW, how do these sealed batteries degrade? Is it sulfating,
or something else? Is there any way to reverse it to some
degree, like charging it with a slightly higher current and/or
voltage, or pulsing it? Again, if the batteries are not 100%
and I only get half of the runtime -- I don't care. But waking
up in the middle of the night because my UPS is beeping
can be highly irritating. :-(


"TheDragon" wrote in message
. ..
I have several modded APC Smart UPS's

Add rear contacts fused and parallel to the internal batteries.
Then you can add any batteries you like as long as the voltage matches the
originals. If you are extending the runtime, very good if you fit a fan to
the grill inside, to cool the ccts inside.
I have a smart APC 1500. It will run at 90% load for 8 hours. No problems
at
all.
P.S I use 4 x exteral Chloride 100AH in a seriel parallel combo to give
the
needed 24v nominal.