diff --git a/plugins/available/battery.plugin.bash b/plugins/available/battery.plugin.bash
index 0391ca10..b9bee172 100644
--- a/plugins/available/battery.plugin.bash
+++ b/plugins/available/battery.plugin.bash
@@ -53,72 +53,31 @@ battery_percentage(){
   about 'displays battery charge as a percentage of full (100%)'
   group 'battery'
 
+  declare COMMAND_OUTPUT="no"
+
   if _command_exists upower;
   then
-    local UPOWER_OUTPUT=$(upower --show-info $(upower --enumerate | grep BAT) | grep percentage | tail --bytes 5)
-    echo ${UPOWER_OUTPUT: : -1}
+    COMMAND_OUTPUT=$(upower --show-info $(upower --enumerate | grep BAT) | grep percentage | grep -o "[0-9]\+" | head -1)
   elif _command_exists acpi;
   then
-    local ACPI_OUTPUT=$(acpi -b)
-    case $ACPI_OUTPUT in
-      *" Unknown"*)
-        local PERC_OUTPUT=$(echo $ACPI_OUTPUT | head -c 22 | tail -c 2)
-        case $PERC_OUTPUT in
-          *%)
-            echo "0${PERC_OUTPUT}" | head -c 2
-          ;;
-          *)
-            echo ${PERC_OUTPUT}
-          ;;
-        esac
-      ;;
-
-      *" Charging"* | *" Discharging"*)
-        local PERC_OUTPUT=$(echo $ACPI_OUTPUT | awk -F, '/,/{gsub(/ /, "", $0); gsub(/%/,"", $0); print $2}' )
-        echo ${PERC_OUTPUT}
-      ;;
-      *" Full"*)
-        echo '100'
-      ;;
-      *)
-        echo '-1'
-      ;;
-    esac
+    COMMAND_OUTPUT=$(acpi -b | awk -F, '/,/{gsub(/ /, "", $0); gsub(/%/,"", $0); print $2}' )
   elif _command_exists pmset;
   then
-    local PMSET_OUTPUT=$(pmset -g ps | sed -n 's/.*[[:blank:]]+*\(.*%\).*/\1/p')
-    case $PMSET_OUTPUT in
-      100*)
-        echo '100'
-      ;;
-      *)
-        echo $PMSET_OUTPUT | head -c 2
-      ;;
-    esac
+    COMMAND_OUTPUT=$(pmset -g ps | sed -n 's/.*[[:blank:]]+*\(.*%\).*/\1/p' | grep -o "[0-9]\+" | head -1)
   elif _command_exists ioreg;
   then
-    local IOREG_OUTPUT=$(ioreg -n AppleSmartBattery -r | awk '$1~/Capacity/{c[$1]=$3} END{OFMT="%05.2f%%"; max=c["\"MaxCapacity\""]; print (max>0? 100*c["\"CurrentCapacity\""]/max: "?")}')
-    case $IOREG_OUTPUT in
-      100*)
-        echo '100'
-      ;;
-      *)
-        echo $IOREG_OUTPUT | head -c 2
-      ;;
-    esac
+    COMMAND_OUTPUT=$(ioreg -n AppleSmartBattery -r | awk '$1~/Capacity/{c[$1]=$3} END{OFMT="%05.2f"; max=c["\"MaxCapacity\""]; print (max>0? 100*c["\"CurrentCapacity\""]/max: "?")}' | grep -o "[0-9]\+" | head -1)
   elif _command_exists WMIC;
   then
-    local WINPC=$(echo porcent=$(WMIC PATH Win32_Battery Get EstimatedChargeRemaining /Format:List) | grep -o '[0-9]*')
-    case $WINPC in
-      100*)
-        echo '100'
-      ;;
-      *)
-        echo $WINPC
-      ;;
-    esac
+    COMMAND_OUTPUT=$(WMIC PATH Win32_Battery Get EstimatedChargeRemaining /Format:List | grep -o '[0-9]\+' | head -1)
   else
-    echo "no"
+    COMMAND_OUTPUT="no"
+  fi
+
+  if [ "${COMMAND_OUTPUT}" != "no" ]; then
+    printf "%02d" "${COMMAND_OUTPUT:--1}"
+  else
+    echo "${COMMAND_OUTPUT}"
   fi
 }
 
diff --git a/test/plugins/battery.plugin.bats b/test/plugins/battery.plugin.bats
new file mode 100644
index 00000000..88e20f25
--- /dev/null
+++ b/test/plugins/battery.plugin.bats
@@ -0,0 +1,371 @@
+#!/usr/bin/env bats
+
+load ../test_helper
+load ../../lib/composure
+
+cite _about _param _example _group _author _version
+
+load ../../plugins/available/battery.plugin
+
+# Sets up the `_command_exists` function so that it only responds `true` if called with
+# the name of the function that was passed in as an argument to `setup_command_exists`.
+# This is used to ensure that the test cases can test the various energy management tools
+# without actually having them. When called like
+#
+# setup_command_exists "pmset"
+#
+# then calling `_command_exists "pmset"` will return `true`,
+# while calling `_command_exists "ioreg"` (or other commands) will return `false`.
+#
+# It's cool that Bash allows to define functions within functions, works almost like
+# a closure in JavaScript.
+function setup_command_exists {
+  success_command="$1"
+
+  function _command_exists {
+    case "$1" in
+      "${success_command}")
+        true
+      ;;
+      *)
+        false
+      ;;
+    esac
+  }
+}
+
+#######################
+#
+# no tool
+#
+
+@test 'plugins battery: battery-percentage with no tool' {
+  setup_command_exists "fooooo"
+
+  run battery_percentage
+  assert_output "no"
+}
+
+#######################
+#
+# pmset
+#
+
+# Creates a `pmset` function that simulates output like the real `pmset` command.
+# The passed in parameter is used for the remaining battery percentage.
+function setup_pmset {
+  percent="$1"
+
+  function pmset {
+    printf "\-InternalBattery-0 (id=12345)	%s; discharging; 16:00 remaining present: true" "${percent}"
+  }
+}
+
+@test 'plugins battery: battery-percentage with pmset, 100%' {
+  setup_command_exists "pmset"
+
+  setup_pmset "100%"
+
+  run battery_percentage
+  assert_output "100"
+}
+
+@test 'plugins battery: battery-percentage with pmset, 98%' {
+  setup_command_exists "pmset"
+
+  setup_pmset "98%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with pmset, 98.5%' {
+  setup_command_exists "pmset"
+
+  setup_pmset "98.5%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with pmset, 4%' {
+  setup_command_exists "pmset"
+
+  setup_pmset "4%"
+
+  run battery_percentage
+  assert_output "04"
+}
+
+@test 'plugins battery: battery-percentage with pmset, no status' {
+  setup_command_exists "pmset"
+
+  setup_pmset ""
+
+  run battery_percentage
+  assert_output "-1"
+}
+
+#######################
+#
+# acpi
+#
+
+# Creates a `acpi` function that simulates output like the real `acpi` command.
+# The passed in parameters are used for
+# 1) the remaining battery percentage.
+# 2) the battery status
+function setup_acpi {
+  percent="$1"
+  status="$2"
+
+  function acpi {
+    printf "Battery 0: %s, %s, 01:02:48 until charged" "${status}" "${percent}"
+  }
+}
+
+@test 'plugins battery: battery-percentage with acpi, 100% Full' {
+  setup_command_exists "acpi"
+
+  setup_acpi "100%" "Full"
+
+  run battery_percentage
+  assert_output "100"
+}
+
+@test 'plugins battery: battery-percentage with acpi, 98% Charging' {
+  setup_command_exists "acpi"
+
+  setup_acpi "98%" "Charging"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with acpi, 98% Discharging' {
+  setup_command_exists "acpi"
+
+  setup_acpi "98%" "Discharging"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with acpi, 98% Unknown' {
+  setup_command_exists "acpi"
+
+  setup_acpi "98%" "Unknown"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with acpi, 4% Charging' {
+  setup_command_exists "acpi"
+
+  setup_acpi "4%" "Charging"
+
+  run battery_percentage
+  assert_output "04"
+}
+
+@test 'plugins battery: battery-percentage with acpi, 4% no status' {
+  setup_command_exists "acpi"
+
+  setup_acpi "4%" ""
+
+  run battery_percentage
+  assert_output "04"
+}
+
+@test 'plugins battery: battery-percentage with acpi, no status' {
+  setup_command_exists "acpi"
+
+  setup_acpi "" ""
+
+  run battery_percentage
+  assert_output "-1"
+}
+
+#######################
+#
+# upower
+#
+
+# Creates a `upower` function that simulates output like the real `upower` command.
+# The passed in parameter is used for the remaining battery percentage.
+function setup_upower {
+  percent="$1"
+
+  function upower {
+    printf "voltage:             12.191 V\n    time to full:        57.3 minutes\n    percentage:          %s\n    capacity:            84.6964" "${percent}"
+  }
+}
+
+@test 'plugins battery: battery-percentage with upower, 100%' {
+  setup_command_exists "upower"
+
+  setup_upower "100.00%"
+
+  run battery_percentage
+  assert_output "100"
+}
+
+@test 'plugins battery: battery-percentage with upower, 98%' {
+  setup_command_exists "upower"
+
+  setup_upower "98.4567%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with upower, 98.5%' {
+  setup_command_exists "upower"
+
+  setup_upower "98.5%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with upower, 4%' {
+  setup_command_exists "upower"
+
+  setup_upower "4.2345%"
+
+  run battery_percentage
+  assert_output "04"
+}
+
+@test 'plugins battery: battery-percentage with upower, no output' {
+  setup_command_exists "upower"
+
+  setup_upower ""
+
+  run battery_percentage
+  assert_output "-1"
+}
+
+#######################
+#
+# ioreg
+#
+
+# Creates a `ioreg` function that simulates output like the real `ioreg` command.
+# The passed in parameter is used for the remaining battery percentage.
+function setup_ioreg {
+  percent="$1"
+
+  function ioreg {
+    printf "\"MaxCapacity\" = 100\n\"CurrentCapacity\" = %s" "${percent}"
+  }
+}
+
+@test 'plugins battery: battery-percentage with ioreg, 100%' {
+  setup_command_exists "ioreg"
+
+  setup_ioreg "100%"
+
+  run battery_percentage
+  assert_output "100"
+}
+
+@test 'plugins battery: battery-percentage with ioreg, 98%' {
+  setup_command_exists "ioreg"
+
+  setup_ioreg "98%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with ioreg, 98.5%' {
+  setup_command_exists "ioreg"
+
+  setup_ioreg "98.5%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with ioreg, 4%' {
+  setup_command_exists "ioreg"
+
+  setup_ioreg "4%"
+
+  run battery_percentage
+  assert_output "04"
+}
+
+@test 'plugins battery: battery-percentage with ioreg, no status' {
+  setup_command_exists "ioreg"
+
+  # Simulate that no battery is present
+  function ioreg {
+    printf ""
+  }
+
+  run battery_percentage
+  assert_output "-1"
+}
+
+#######################
+#
+# WMIC
+#
+
+# Creates a `WMIC` function that simulates output like the real `WMIC` command.
+# The passed in parameter is used for the remaining battery percentage.
+function setup_WMIC {
+  percent="$1"
+
+  function WMIC {
+    printf "Charge: %s" "${percent}"
+  }
+}
+
+@test 'plugins battery: battery-percentage with WMIC, 100%' {
+  setup_command_exists "WMIC"
+
+  setup_WMIC "100%"
+
+  run battery_percentage
+  assert_output "100"
+}
+
+@test 'plugins battery: battery-percentage with WMIC, 98%' {
+  setup_command_exists "WMIC"
+
+  setup_WMIC "98%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with WMIC, 98.5%' {
+  setup_command_exists "WMIC"
+
+  setup_WMIC "98.5%"
+
+  run battery_percentage
+  assert_output "98"
+}
+
+@test 'plugins battery: battery-percentage with WMIC, 4%' {
+  setup_command_exists "WMIC"
+
+  setup_WMIC "4%"
+
+  run battery_percentage
+  assert_output "04"
+}
+
+@test 'plugins battery: battery-percentage with WMIC, no status' {
+  setup_command_exists "WMIC"
+
+  setup_WMIC ""
+
+  run battery_percentage
+  assert_output "-1"
+}
diff --git a/test/run b/test/run
index dab65268..da1aa061 100755
--- a/test/run
+++ b/test/run
@@ -10,4 +10,10 @@ if [ -z "${BASH_IT}" ]; then
   export BASH_IT
 fi
 
-exec $bats_executable ${CI:+--tap} ${test_directory}/{bash_it,completion,install,lib,plugins,themes}
+if [ -z "$1" ]; then
+  test_dirs=( ${test_directory}/{bash_it,completion,install,lib,plugins,themes} )
+else
+  test_dirs=( "$1" )
+fi
+
+exec $bats_executable ${CI:+--tap} "${test_dirs[@]}"