Button cells are small, disk-shaped batteries that provide lw current over a long period. The diameter and thickness of a button cell varies according to the model. These batteries generate a voltage from 1.5 to 3 volts.
They are therefore ideal for stand-alone devices that must operate over long periods of time, such as watches or wireless alarms.
Button cells, a threat to the environment
Often, button cell batteries sold commercially function using a metallic lithium anode and a manganese oxide cathode (MnO2). Some also contain mercury, a toxic heavy metal that has been removed from other types of batteries. Other types are alkaline or based on silver-zinc.
Their small size and the toxic metals they contain make button cell batteries potentially dangerous to children, who may swallow them, and to the environment.
3V lithium button cell. © Krzysztof Woznica, Wikimedia public domain