In an interview with AllThingsD, Apple VP Michael Tchao has explained in some detail the charging process on the iPad, iPhone, and iPod touch.
According to Tchao, all iOS devices do in fact display a 100 percent charge just prior to reaching a complete charge, at which point it will continue charging to 100 percent, then discharge slightly and charge back up, repeating the process for as long as the device is connected.
“That circuitry is designed so you can keep your device plugged in as long as you would like,” Tchao said, adding that the process allows devices to maintain an optimum charge.
