gistfile1.lua

mybattery = widget({ type="textbox"})
...
mywibox[s].widgets = {
  ...
  mybattery,
  ...
}
mytimer = timer({ timeout = 30 })
-- i am sorry...
mytimer:add_signal("timeout", function () mybattery.text = io.popen("acpi | sed -e 's/Battery [0-9]: //' -e's/until charged//' -e 's/remaining//' -e's/ //g' -e 's/,/ /g'"):read() end)
mytimer:start()