Final answer:
An ammeter is an instrument used to measure the rate of flow of electric current. In a battery charging system, the ammeter is used to indicate the current flowing through the circuit during charging.
Step-by-step explanation:
An ammeter is an instrument used to measure the rate of flow of electric current in a circuit. It is connected in series with the component or circuit it is measuring. The purpose of an ammeter in a battery charging system is to indicate the current flowing through the circuit during the charging process.