For a recent battery powered ESP8266 project I needed a closeable box with an On/Off-button. It might be reused for other chargeable electronics projects.
You can put a 18650 battery holder inside and hot glue it to the box.
To charge the battery, there's a hole for a 18650 micro usb charger. (something like http://www.ebay.de/itm/311572862117). Hot glue it into the right place and you can charge the 18650 battery with micro usb.
As a power button I used the following item I found on ebay: http://www.ebay.de/itm/191574665101
I connected the power of the led in the switch via a transistor with the ESP so I can control the light programmatically