The version of this board in box is named ESP8266-EVB-BAT-BOX is perfect if you want to make handheld WiFi gadgets :
As name saysESP8266-EVB-BAT is exclusively designed to may work on battery. It have input voltage sense, build-in intelligent charger for LiPo battery and battery connector, so you can use any of our existing LiPo batteries for your next handheld WIFI device.
The battery charges can charge with 200 or 400mA and selectable by SMT jumper on the board. On board there is also step-up converter which provide 5V power supply to the relay and module. So if battery is attached and external power is applied the charger will charge the Lipo battery to maximum, then if external power is cut the battery will automatically supply power to the board. GPIO16 input is connected and sense external power supply.