Batteries were invented in 1800, but their complex chemical processes are still being explored and improved. While there are several types of batteries, at its essence a battery is a device that converts chemical energy into electric energy.

Fentanyl analogs are illicit—and often deadly—alterations of the medically prescribed drug fentanyl. The analogs have similar—but not the same—chemical structure, and they mimic the pharmacological effects of the original drug.