Package: gir1.2-upowerglib-1.0
Version: 1:0.9.23-2+devuan1.3

On Devuan Beowulf, the Cinnamon Power Management (and therefore also the battery indicator applet) fail to read updated information from the system.

The script that handles this is cs_power.py, which is a module called by cinnamon-settings.py. I have pared it down to the bare minimum lines to return the battery percentage and state:

###################################################################
#!/usr/bin/python3

import gi
gi.require_version('CinnamonDesktop', '3.0')
gi.require_version('UPowerGlib', '1.0')
from gi.repository import CinnamonDesktop, Gdk, UPowerGlib, Gio

(UP_ID, UP_VENDOR, UP_MODEL, UP_TYPE, UP_ICON, UP_PERCENTAGE, UP_STATE, UP_SECONDS) = range(8)

up_client = UPowerGlib.Client.new()

csd_power_proxy = Gio.DBusProxy.new_sync(
    Gio.bus_get_sync(Gio.BusType.SESSION, None),
    Gio.DBusProxyFlags.NONE,
    None,
    "org.cinnamon.SettingsDaemon.Power",
    "/org/cinnamon/SettingsDaemon/Power",
    "org.cinnamon.SettingsDaemon.Power",
    None)

devices = csd_power_proxy.GetDevices()
for device in devices:
    if device[UP_TYPE] == UPowerGlib.DeviceKind.BATTERY:
        batdevice = device
percentage = batdevice[UP_PERCENTAGE]
state = batdevice[UP_STATE]

print(percentage)
print(state)
###############################################

The result, when I ran it, showed 89% and discharging whereas $(upower -i /org/freedesktop/UPower/devices/battery_BAT0) returned 58% and charging. Therefore the issue is with UPowerGlib, which is provided by the package gir1.2-upowerglib-1.0

Current software versions:

Lenovo Thinkpad T480s
Linux Josh-Laptop 4.19.0-8-amd64 #1 SMP Debian 4.19.98-1 (2020-01-26) x86_64 GNU/Linux
Devuan Beowulf
gir1.2-upowerglib-1.0/now 1:0.9.23-2+devuan1.3 amd64
cinnamon-settings-daemon/testing,now 3.8.4-2 amd64
upower/now 1:0.9.23-2+devuan1.3 amd64