Final answer:
Secondary batteries, also known as rechargeable batteries, should be marked to differentiate them from primary, non-rechargeable batteries, and adhere to environmental regulations like Directive 2006/66/EC of the European Union.
Step-by-step explanation:
Batteries used as a secondary power supply, also known as rechargeable or secondary batteries, should be permanently marked to distinguish them from non-rechargeable, or primary, batteries. This marking is essential because rechargeable batteries can be recharged by applying an electrical potential in the reverse direction, which converts the battery from a galvanic cell to an electrolytic cell. This process enables the insoluble product that adheres to the electrodes during discharge to be removed, thus restoring the battery's capacity
Furthermore, it's essential to understand that these batteries adhere to certain environmental regulations like Directive 2006/66/EC of the European Union, which prohibits placing on the market portable batteries containing more than 0.002% of cadmium by weight, aimed at improving the environmental performance of batteries and accumulators. Such regulations and performance standards necessitate clear and permanent markings on batteries to ensure proper usage and disposal. This ensures users can differentiate between the types and also adhere to environmental safety and recycling guidelines.