Battery current charging measurment
I did not understand how does this ciruict works! *Why have we used R24=1.2M? Especially in case we remove R21 (As it is noted by DNP)


Recall, that this is circuit is both a battery charger and power supply, so the battery current is bi-directional. When operating as a power supply the battery is discharging and the current-shunt output potential is below PGND.

The role of R24 is to bias the output of the current shunt above ground on this single supply design. Resistors R24 and R16 form a voltage divider that bias the current shunts potential up by approximately 200 mV (if I am reading the supply rail correctly as 5VDC).

The remaining components would be selected for filtering and loop compensation of the constant current control loop.