Based on Patricks code (http://forum.mysensors.org/topic/2700/sct-013-030-energy-meter).
Rewrote and cleaned up original code to allow for Sleeping between power readings every minute. Uses approximately 80% less power this way. (22ma down to 4.6ma on pro mini 3.3v) Adjusted sleep duration to cater for node computation time. Time drift reduced to 2ms/minute.
Added battery voltage reporting (does not require any additional hardware, only VCC library from https://github.com/Yveaux/arduino_vcc
To do: Figure out how to save KWh readings between resets as mentioned by Patrick
