awesome-wm-widgets/battery-widget/battery.lua

local wibox = require("wibox")
local awful = require("awful")
local naughty = require("naughty")
local watch = require("awful.widget.watch")

battery_widget = wibox.widget { widget = wibox.widget.imagebox }

-- acpi sample outputs
-- Battery 0: Discharging, 75%, 01:51:38 remaining
-- Battery 0: Charging, 53%, 00:57:43 until charged

local path_to_icons = "/usr/share/icons/Arc-Icons/panel/22/"

watch(
    "acpi", 10,
    function(widget, stdout, stderr, exitreason, exitcode)
        local batteryType
        local _, status, charge, time = string.match(stdout, '(.+): (%a+), (%d%d)%%, (.+)')
        charge = tonumber(charge)
        if (charge >= 0 and charge < 20) then 
            batteryType="battery-empty"
            show_battery_warning()
        elseif (charge >= 20 and charge < 40) then batteryType="battery-caution"
        elseif (charge >= 40 and charge < 60) then batteryType="battery-low"
        elseif (charge >= 60 and charge < 80) then batteryType="battery-good"
        elseif (charge >= 80 and charge <= 100) then batteryType="battery-full"
        end
        if status == 'Charging' then 
            batteryType = batteryType .. '-charging'
        end
        battery_widget.image = path_to_icons .. batteryType .. ".svg"
    end
)

function show_battery_status()
    awful.spawn.easy_async([[bash -c 'acpi']],
        function(stdout, stderr, reason, exit_code)   
            naughty.notify{
                text = stdout,
                title = "Battery status",
                timeout = 5, hover_timeout = 0.5,
                width = 200,
            }
        end
    )
end

function show_battery_warning()
    naughty.notify{
    text = "Huston, we have a problem",
    title = "Battery is dying",
    timeout = 5, hover_timeout = 0.5,
    position = "bottom_right",
    bg = "#F06060",
    fg = "#EEE9EF",
    width = 200,
}
end

-- popup with battery info
battery_widget:connect_signal("mouse::enter", function() show_battery_status() end)