Description 
This breakout is capable of constantly monitoring the current of the sensor. It can add it up and will give you a pulse, each time, a given amount of amp-hours has been used. If you use the module effectively, you’ll always know exactly how much of charge is left!
At one end of the Coulomb Counter, Breakout is headers labeled IN and OUT. Connect your battery or power supply to the IN header or JST battery connector (they’re identical.), and connect the OUT header to your project. At the other end of the Coulomb Counter, you’ll find a header with six pins. These are the pins you’ll need to connect to your microcontroller and include VIO (Voltage Input), INT (interrupt), POL (Polarity), GND (ground), CLR (Clear), and SHDN (shutdown). Simply install this breakout out between your power source and your circuit, that all circuit current needs to pass through the Coulomb Counter to be measured.
The LTC®4150 measures battery depletion and charging in handheld PC and portable product applications. The device monitors the current through an external sense resistor between the battery’s positive terminal and the battery’s load or charger. A voltage-to-frequency converter transforms the current sense voltage into a series of output pulses at the interrupt pin. These pulses correspond to a fixed quantity of charge flowing into or out of the battery. The part also indicates charge polarity as the battery is depleted or charged. 
The LTC4150 is intended for 1-cell or 2-cell Li-Ion and 3-cell to 6-cell NiCd or NiMH applications.

Features
Chip: LTC4150
Operating Voltage: 2.7V ~ 8.5V
Operating Current: 1A
Indicates Charge Quantity and Polarity
Sense Voltage Range: ±50mV
Charge Count Frequency: 32.55Hz/V
Shutdown Current: 1.5μA
Pin number: 10 Pins

 

Resources:

Datasheet

Measuring current draw with LTC4150 + ESP-12E

SparkFunCoulomb Counter Breakout - LTC4150

 

LTC4150 - Coulomb Counter, LTC4150 Battery Charge Current Detection

USh30,000Price