Why can't charge levels be determined solely by checking the electrolyte specific gravity in nickel-cadmium batteries?

Determining charge levels solely by checking the electrolyte specific gravity in nickel-cadmium batteries is problematic because no appreciable changes occur in specific gravity during the charge or discharge cycles. Unlike lead-acid batteries, where the specific gravity changes significantly as the battery is charged or discharged, nickel-cadmium batteries maintain a relatively stable specific gravity throughout their operational cycles. This means that merely measuring the specific gravity of the electrolyte would not provide a reliable indication of the battery's state of charge or state of health.

To accurately assess the state of charge in nickel-cadmium batteries, other methods must be employed, such as using voltmeters or specific charge testing methodologies. Understanding this characteristic of nickel-cadmium batteries is crucial for proper maintenance and operation, ensuring the reliability and longevity of these power sources.