This cable can only be used on voltage-signalling UPSes, and apparently only provides the On Battery signal. As a consequence, this cable is pretty much useless, because all APC UPSes support more than just On Battery.
Signal Computer UPS DB9F DB9M DCD 1 -------------------- 2 On Battery 3.3K ohm TxD 3 --[####]-* | DTR 4 ---------* GND 5 ---------------*---- 4 Ground | *---- 9 Common