Coin Cell Battery for Arduino/Microcontroller
The Arduino Uno isn't fit to run off a coin cell.  


The Uno isn't exactly low-power. It contains 2 microcontrollers running at high clock frequencies and consumes a couple tens of mA
A coin cell will give you 3 V, while the Uno is designed to run on 5 V. 
Most important: a coin cell has enough energy to power the Arduino for a couple of hours, but can only supply this in small doses, i.e. a few mA. That won't work.