My battery widget for AwesomeWM on my Laptop. If you want this to work on your machine, you might need to make substantial changes. This widget targets Awesome 3.4.

battery_widget.lua

-- Create a battery widget
mybatterywidget = widget({type="textbox"})

-- do not forget to add the widget to your panel ;-)

-- display the current charge (in %) and the charging/discharging rate (in W) 
-- for the battery identified by <adapter>
function show_battery(adapter)
	local fcur = io.open("/sys/class/power_supply/"..adapter.."/charge_now")	
	local fcap = io.open("/sys/class/power_supply/"..adapter.."/charge_full")
	local fvolt = io.open("/sys/class/power_supply/"..adapter.."/voltage_now")
	local famp = io.open("/sys/class/power_supply/"..adapter.."/current_now")
	if fcur and fcap and fvolt and famp then
		local cur = fcur:read()
		local cap = fcap:read()
		local battery = math.floor(cur * 100 / cap)
		local volt = fvolt:read()
		local amp = famp:read()
		local watts = string.format("%.2f",(volt/1000000)*(amp/1000000))
		text = battery.."% "..watts.."W"
		fcur:close()
		fcap:close()
		fvolt:close()
		famp:close()
	else
		text = "n.a."
	end
	mybatterywidget.text = text
end

-- create a timer to update the widget periodically
battery_timer = timer({timeout = 20})
battery_timer:add_signal("timeout", function()  show_battery("BAT0") end)
battery_timer:start()
show_battery("BAT0") --run the function once on startup of the window manager so we don't have to wait for the timer