Turn off your Nexto and connect AC adapter to the port of [DC-IN] at the bottom of Nexto. The LED around the button will light red to indicate that Nexto is being charged. When done, the red light will be turned off.
If you want to charge external battery, connect external battery to [BAT] port while AC adapter is connected.
[e] icon means [now charging]. if you can;t see [e] while connecting, maybe there is something wrong in charging part.