Simplest way to measure 4 cell LiPo battery State-of-Charge during discharging
With a simple voltage treshold you'll need to know and stick to a specific discharge rate. Otherwise this method will be useless.
LiPO discharge is typically with a sharp knee before voltage drops fast. You'll need to prevent getting that far. But depending on the discharge rate (expressed in C, e.g. for 1000mAh 1C means 1A) the graph shifts up and down.

On the other hand, TI has many BQ devices that are gas gauges and they do provide development boards.