The cords used on radios, televisions, and other electronics are 18ga or 16ga copper wire encased in plastic. It's a little known fact that every year those cords lose 10% of their electrons. By the 7th or 8th year, these cords are incapable of providing enough power to the electronic devices, which causes the electronics to fail. After ten years, these cords can hardly transfer any electric current, because there are few electrons left to carry the current. At this stage, all electronics fail due to a lack of proper voltage and amperage coming from the power source.
There is no known way to replenish the electrons in these copper cords, so they must be replaced at least every five years. It's recommended to replace them every three years on costly equipment to eliminate electronic component failure.
You can increase the life span of cords by using a thicker copper wire, such as 12ga or 10ga, but it is still recommended that they be replaced at least every eight years.