[DNSB]

Played on my Libra Colour and changed battery to bd71827_bat in the shell script. I've attached the script (renamed to battcalc.sh.txt so rename back) and an image of the popup.

My first pass at the changes screwed up when I copy/pasted the script and the line endings were changed to CRLF. Used Notepad++ to change them to LF and all was happy.

Spoiler:

# Battery Statistics Calculator 1.0 (2023-05-18) by Aleron Ives
#
# This script calculates battery statistics for the Kobo Libra 2.
# Check the contents of /sys/class/power_supply/ if you use a different
# model to ensure that the statistics you want to track are available.
# 
# For the Libra Colour, you need to use bd71827_bat instead of battery.
# 
# You can use NickelMenu to invoke this script like so:
# menu_item :main :Battery :cmd_output :500 :/mnt/onboard/.adds/battcalc.sh
# 
# Gather the necessary statistics
# 
meter=$(cat /sys/class/power_supply/bd71827_bat/capacity)
v_now=$(cat /sys/class/power_supply/bd71827_bat/voltage_now)
v_min=$(cat /sys/class/power_supply/bd71827_bat/voltage_min)
v_max=$(cat /sys/class/power_supply/bd71827_bat/voltage_max)
c_now=$(cat /sys/class/power_supply/bd71827_bat/charge_now)
c_full=$(cat /sys/class/power_supply/bd71827_bat/charge_full)
c_dfull=$(cat /sys/class/power_supply/bd71827_bat/charge_full_design)

let v_now/=1000; let v_min/=1000; let v_max/=1000 # Convert to V
let c_now/=1000; let c_full/=1000; let c_dfull/=1000 # Convert to mAh
let v_nowr=$v_now%1000; let v_now/=1000 # Simulate floating-point arithmetic
let v_minr=$v_min%1000; let v_min/=1000 # "
let v_maxr=$v_max%1000; let v_max/=1000 # "
let charge=$c_now*100/$c_full # Calculate charge percentage from mAh
let c_health=$c_full*100/$c_dfull # Calculate health percentage from mAh

# Format and display the results

echo Capacity: $c_now mAh / $meter% / $charge%
echo Voltage: $v_min.$v_minr V / $v_now.$v_nowr V / $v_max.$v_maxr V
echo Health: $c_full mAh / $c_dfull mAh / $c_health%