Which device is used to measure the charge of a storage battery?

The most appropriate device for measuring the charge of a storage battery is the hydrometer. This instrument assesses the specific gravity of the electrolyte in lead-acid batteries, which is a direct indication of the battery's state of charge. The specific gravity will increase as the battery charges, reflecting a higher concentration of sulfuric acid in the electrolyte solution.

Using a hydrometer, a technician can quickly determine how fully charged the battery is by comparing the measurement obtained with standard specific gravity values for fully charged and discharged states. This makes it particularly useful for lead-acid batteries commonly found in many applications.

While a voltmeter can measure the voltage of a battery and provide some indication of its charge level, it does not give a complete picture of the battery's state of charge as affected by the condition of the electrolyte. An ammeter measures current flow, and while helpful in analyzing the system's performance, it doesn't indicate charge levels. A multimeter can also measure voltage, current, and resistance, but lacks the specific capacity to determine the state of charge of a storage battery directly.