Hello all,
Everything is in the title, i want to supply an arduino mini and about 30 leds (low consumption thanks to PWM) using the smallest battery as possible, the CR2354 battery (3v 500mah) seems to be ok if i put 2 or 3.
Someone can confirm ? I'm not an electronic expert ...
Thanks 
You would need 2 in series to provide a sufficient voltage if it's a 16 mhz pro mini.
How much current are those LEDs drawing?
Those coin cell batteries don't perform very well under much of a load, I suspect if it works, you'll have disappointing battery life.
Don't try 16MHz, 8MHz takes half the current. The lower the voltage the lower the current
too, so if you set the brown-out fuses to 1.8V instead of 2.7V and run from a few of those
cells in parallel, it might work. They only produce a couple of mA each.
For driving LEDs I'd forget 3V lithium calculator batteries and use LR44 alkaline button
cells, 2 or 3 in series can produce far more current.