The circuit is centered around a TL431 programmable shunt regulator ... He tested the output current into a half-charged battery to verify that he was in the right ballpark.

The INA219 is a current shunt and power monitor IC with an I²C ... Not only that, he replaced the 4 LEDs that were the battery level indicators and actually consume more amps than his board ...

Vishay is also spotlighting key products from its recent acquisition of Ametherm, such as state-of-the-art inrush current limiters ... and Power Metal Strip® battery shunts.