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

How easy is to do the link between my Arduino Yun and one mobile using free soft Blynk.

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

Temboo is very easy to automate the IoT with Arduno YUN, in combination with Blynk and Dropbox to store pictures. All is free and easy.

RPMA backhaul for Arduino Yun + Temp / Humidity sensor

RPMA Backhaul + Arduino Yun – Part 3 of 3

2nd portion of RPMA + Arduino Yun (2 of 3)

Fast function getDS1307timeStamp().

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