What is AC adapter (charger)?

As you know, the smartphone is running on a built-in battery, so it goes without saying that if you are using it the battery will be exhausted and you will not be able to use it at the end. A rechargeable battery (this is called a secondary battery) is built in the smartphone and it is common to connect the AC adapter (charger) and charge it into the built-in battery.

The AC adapter converts AC outlet (Ex. voltage of 100 V in Japan) into DC (direct current voltage of about 5 V) required for operation (charging) of the smartphone.