.bashrc to show battery percentage at prompt

Code:
#
# ~/.bashrc
#

# If not running interactively, don't do anything
[[ $- != *i* ]] && return

alias ls='ls --color=auto'

battery_status(){
  # From http://www.basicallytech.com/blog/archive/110/Colour-coded-battery-charge-level-and-status-in-your-bash-prompt
  BATTERY=/sys/class/power_supply/axp20x-battery

  BATSTATE=$(cat ${BATTERY}/status)
  CHARGE=$(cat ${BATTERY}/capacity)

  NON='\033[00m'
  BLD='\033[01m'
  RED='\033[01;31m'
  GRN='\033[01;32m'
  YEL='\033[01;33m'

  COLOUR="$RED"

  case "${BATSTATE}" in
     'Charged')
     BATSTT="$BLD=$NON"
     ;;
     'Charging')
     BATSTT="$BLD+$NON"
     ;;
     'Discharging')
     BATSTT="$BLD-$NON"
     ;;
  esac

  # prevent a charge of more than 100% displaying
  if [ "$CHARGE" -gt "99" ]
  then
     CHARGE=100
  fi
  
  if [ "$CHARGE" -gt "15" ]
  then
     COLOUR="$YEL"
  fi
  
  if [ "$CHARGE" -gt "30" ]
  then
     COLOUR="$GRN"
  fi
  
  echo -e "${COLOUR}${CHARGE}%${NON} ${BATSTT}"
}


PS1='[$(battery_status)][\u@\h \W]\$ '