/etc/apcupsd/apcupsd.confを編集

...
UPSCABLE usb
...
UPSTYPE usb
# DEVICE /dev/ttyS0
DEVICE
...
# TIMEOUT 0
TcIMEOUT 60
...

/etc/default/apcupsdを編集．

# Defaults for apcupsd initscript (unused with systemd as init).
# Set to "yes" to enable startup of apcupsd.
#ISCONFIGURED=no
ISCONFIGURED=yes

# apctest

2020-12-17 17:35:07 apctest 3.14.14 (31 May 2016) debian
Checking configuration ...
sharenet.type = Network & ShareUPS Disabled
cable.type = USB Cable
mode.type = USB UPS Driver
Setting up the port ...
apctest FATAL ERROR in apctest.c at line 321
Unable to open UPS device.
  If apcupsd or apctest is already running,
  please stop it and run this program again.
apctest error termination completed