I ended up using a DB-9 to RJ-45 adapter, then wired it to the Cisco console pinout. That let me use a regular Cisco console cable to connect to mine. Already had the Cisco cable, the adapter was a few bucks.
Here's the adapter I bought on amazon.com:
StarTech.com DB9 to RJ45 Modular Adapter - M/F - Serial adapter - DB-9 (M) to RJ-45 (F) - GC98MF,Gray
Yeah, the serial ports on APC UPSes have a proprietary pinout. It's a pain to deal with, especially since plugging in a regular serial cable can cause the UPS to shutdown.
IMHO the best thing to do is get a DB9 to RJ-45 adapter and wire it up to the Cisco console pinout, and then just use a Cisco console cable (like the rest of the serial gear in my rack, for consistency). Then you never have to worry about the pinout again.
This is the adapter I used: https://smile.amazon.com/dp/B00066HL3W
And the console cable: https://smile.amazon.com/dp/B07BK6P67K