I have 3 Best Fortress 950 kva UPS units I picked up surplus over 10
years ago. All date codes I can find on them show they were made in
1992. One unit is still operating on it's original batteries! I
haven't done a long duration load test but I'm sure it wouldn't last
long with batteries that old. It does a good job of keeping a computer
from shutting down on short duration power hits.

The other two units I have running on external batteries I picked up
surplus. Originally these units had four 6 volt 12 amp hour batteries.
One of these I have modified for external batteries and is running on
two 93 amp hour 12 volt Dynasty batteries in series. This unit powers a
server, emergency lighting and security cameras in a small business. A
long duration load test was done unintentionally on this unit. A
commercial power hit caused by a nearby lightning strike tripped the
ground fault breaker the ups was connected to. Our alarm system ac
power fail circuit was connected to a different circuit breaker than the
ups so we didn't get a power fail notification. That has been
corrected. This just happen to occur on a Friday evening so the ups ran
until it shut down on low voltage approximately 12 hours later.

These units have a built in fan and will power on without ac connected.
I have used the unit which has it's original batteries for powering
radio test equipment while in the field and mobile. I haven't viewed
output wave form from these units but I'm fairly sure they don't
provide a true sine wave output. However so far these units have
powered everything I've needed them to. Even an old HP Laser Jet printer.

I just checked the no load battery current drain on one unit and found
it to be 1.45 amps with the batteries at 13.72 volts each. So the idle
battery drain is very close to 40 watts. That's with the fan running
because the fan comes on as soon as the inverter starts.