- With the bootloader
There are three different power-related pins: GND, VCC, and RAW. GND, obviously, is the common/ground/0V reference. RAW is the input voltage that runs into the regulator. The voltage at this input can be anywhere from 3.4 to 12V. The voltage at VCC is supplied directly to the Pro Mini, so any voltage applied to that pin should already be regulated to 3.3V.
Using on battery power
- Lower the brown out detection (BOD) to 1.8V
- Remove the voltage regulator
- Remove the power LED and/or its series resistor
Complete info at http://www.gammon.com.au/power