In all my years, never tried to run a pic with a battery. Have some 12F508 and will use a couple of AAA batteries.
It's for an outdoor project and the pic will only power up with a water level switch, so essentially great battery life.

3v performs well in the extremes of winter? Like I say, never used a battery on a pic. Should I opt for 3.3v? or 3 aaa?
Datasheet says as low as 2v (!) for Vcc