Very well put! I actually use my N9 as a semi-dumbphone during travel when I know I may be away from the wall charger for unknown periods.

I basically disable internet connection- connect it only when I am going to need it. Exit wazapp etc. I have LPM on with double tap to wake screen, and network is set to use 2G only.

This mode gives me about 2 days plus a few hours, with 30mins of calling approx and few google address lookups per day.