A simple and inexpensive solution is to use a 'mobile power bank'

Back up a file stored on an SD card to Dropbox automatically.

For Arduino Yùn, adds new REST commands, enabling tunnelling for I2C messages.

Best in class Arduino Yun controller.

Fast function getDS1307timeStamp().

Arduino-library-I2CtunnelW - For Arduino Yùn, adds new REST commands, enabling tunnelling for I2C messages.