Answer:
Electrical charge, q = 75 C
Step-by-step explanation:
It is given that,
Voltage, V = 4 V
Energy stored, E = 300 J
Energy stored in the battery is given by :

q is the electrical charge


q = 75 C
So, the electrical charge of 75 C must flow between the battery's terminals to completely drain the battery if it is fully charged. Hence, this is the required solution.