Rechargeable batteries result in longer life span which results in less need for as many batteries. This is accomplished because the chemical reaction that creates the electrical energy can be reversed. Rechargeable batteries usually have a higher initial cost and require a battery charger. However, this initial investment may be recovered. Each rechargeable battery may substitute hundreds of primary batteries and cost much less than the primary batteries it replaces over its life.
Most technologies developed by humans have positive as well as negative impacts.
However, even these batteries must be eventually replaced. When they are thrown out, the environmental release of cadmium poses potential health threats. Cadmium can accumulate in the environment by leaching from landfills into ground water and surface water. It can also enter the atmosphere if the Ni-Cd battery is burned. Cadmium is toxic to fish and wildlife and can be passed to humans through the food chain.