Dual battery status in screen hardline

.screenrc

# This set's a shell command with the ID #1,
# results expire every 15 seconds,
# and new results are fetched 1 second after expiration.
backtick 1 15 1 battery.sh

# I do this because I know it works
hardstatus alwayslastline

# Here's my current hardline:
hardstatus string "%{= rk} %{W}%H  %{k}[ %{=kw}%-Lw%{r}(%{W}%n*%f%t%{r})%{k}%+Lw%= %{k}]%{-b W} [%{k r}%1`] %0C:%s %{g}"

# The key part of that hardline is where we format and display the result from the 'backtick' command (earlier)
#     [%{k r}%1`]
#     White text (k), red background (r), output from backtick id (#1)

# Example display:
#  deepfryer  [ (0*z)                                            ] [⚡] 12:54:17   
#                                                                   ^- battery is charging
#  deepfryer  [ (0*z)                                    ] [90.0/100.0%] 12:54:59 
#                                                             ^    ^---------------- Built-in battery charge
#                                                             +--------------------- Pluggable battery charge


# IMPORTANT PART:
# [%{k r}%1`]

bin.battery.sh

#!/bin/bash

CHARGING='⚡'
# Pluggable battery
CHARGE_NOW1=`cat /sys/class/power_supply/BAT1/energy_now`
CHARGE_MAX1=`cat /sys/class/power_supply/BAT1/energy_full`
STATUS1=`cat /sys/class/power_supply/BAT1/status`

# Built-in battery
CHARGE_NOW0=`cat /sys/class/power_supply/BAT0/energy_now`
CHARGE_MAX0=`cat /sys/class/power_supply/BAT0/energy_full`
STATUS0=`cat /sys/class/power_supply/BAT0/status`


CHARGE_NOW_SUM=$(( ${CHARGE_NOW1} + ${CHARGE_NOW0} ))
CHARGE_MAX_SUM=$(( ${CHARGE_MAX1} + ${CHARGE_MAX0} ))

# These commented out ones are just for debugging!!!

# echo -n "Pluggable battery % remaining: "
# echo "scale=1; (${CHARGE_NOW1}/${CHARGE_MAX1}) * 100" | bc
# echo -n "Built-in battery % remaining: "
# echo "scale=1; (${CHARGE_NOW0}/${CHARGE_MAX0}) * 100" | bc
# echo -n "Pluggable+Built-in battery % remaining: "
# echo "scale=1; (${CHARGE_NOW_SUM}/${CHARGE_MAX_SUM}) * 100" | bc

# Print the text which will appear in the hardline backtick
if [ "${STATUS1}" = "Charging" ]; then
    echo -n ${CHARGING}
else
    CHARGE1=`echo "scale=1; (${CHARGE_NOW1}/${CHARGE_MAX1}) * 100" | bc`
    CHARGE0=`echo "scale=1; (${CHARGE_NOW0}/${CHARGE_MAX0}) * 100" | bc`
    echo -n "${CHARGE1}/${CHARGE0}%"
fi