An AC adapter is a device that converts voltage into a lower voltage, typically DC, for example, to charge a mobile phone or notebook. One can also use it for the connection of a device which can also operate on batteries. Such an adapter may be integral with a plug, which sometimes can be difficult in multiple sockets. The DC voltage from an AC adapter is not exactly equal to those of batteries, there are devices that do run on batteries, but do not run at the same DC voltage from an AC adapter.