Rechargeable batteries are devices for making electricity portable. Periodic insertion in a charging device plugged into an electrical current allows the same battery to be used repeatedly to power small electrical devices.
Small versions of these useful items aid in defraying the cost of running tape players and radios, while the more exotic forms of rechargeable battery are used to power cellular telephones and laptop computers. While regular batteries have been around for decades, the rechargeable variety remove the need for regular investment in metals and acid, which which can amount to a lot over the lifetime of even a single portable electronic product.
There are health risks associated with the use of rechargeable batteries. The traditional form uses a nickel-cadmium combination of metals that, over time, due either to laziness or malevolence, begins refusing to hold a charge. Batteries thus affected do their level best to mix in with still-functioning units, increasing the chances that any given set of batteries pulled out of a drawer will be useless. The risk to health comes from brain-overload suffered in trying to keep track of which battery combinations have been tested, and from the temptation to fling the tiny cylinders of malignance against the nearest wall until they explode and spray corrosive chemicals everywhere. The 9-volt variety, carried in a hip pocket, has a tendency to attract keys, which bridge the leads to form a circuit, consequently the battery becomes rapidly dangerously hot.