How can I make a low battery indicator for a 7.4 Li ion battery?

I'm hoping somebody can help show me how to make one or help me find a schematic for one as I have no Idea where to look, Google search is overwhelming and none of the results are for a similar battery (and are too complex). I really only need a circuit with one LED that lights up when the voltage drops, nothing fancy.
   
The battery is 7.4 V as stated and is Li ion.

The reason you can't find a simple one, is because it isn't simple to detect when a Lion battery is going flat. They have a "flat discharge" characteristic, which means that the output voltage stays very close to 7.4 volts until it is almost flat.

Lion battery chargers rely on measuring the current that flows in and out over time to determine how full the cell is.

Steve