My lowest power sketch for the ATMEGA328P / Arduino Nano v3 About 200 nA @ Deep sleep with interrupt wake
Because it is very well possible to make the Arduino Nano v3 run at low power levels with some hardware tweaks and a useful pattern I provide this slim sketch supplementary to my youtube "tutorial":
https://www.youtube.com/watch?v=plkn13dOgpU
I hope this helps you in your low-power journey.
Regards,
Eric