Which statement is true about secondary cells compared to primary cells?

Secondary cells, also known as rechargeable batteries, have the key characteristic of being reused multiple times. This is due to their ability to be recharged through an external power source, allowing them to go through numerous charge and discharge cycles. Because of this feature, secondary cells are often preferred for applications where long-term energy storage and repeated use are required, such as in electric vehicles, smartphones, and laptops.

In contrast, primary cells are single-use batteries that cannot be recharged once depleted. Their design is geared towards providing energy until they are exhausted, which makes the ability to recharge a critical advantage of secondary cells. This distinction is essential in understanding the efficiency and practicality of energy storage and usage in various applications.

The other statements present comparisons that generally do not apply when distinguishing between secondary and primary cells. For instance, while secondary cells may sometimes be more expensive to produce, their long-term use typically offsets the initial cost; energy density can vary based on specific chemistry; and efficiency in energy conversion can depend on numerous factors beyond just the cell type.