Load FRF57 froyo. Install a low voltage kernel. Set it to 125 MHz - 600 Mhz OnDemand. Now switch off data (Use any cut), switch off GPS, BT, WiFI (use stock power widget), set screen brightness to min (use stock power widget). Keep your phone usage to minimum, say only a few minutes per day. Do not use data. The battery can last up to 10 days. Mine lasted for 9 and half days with about 20 minutes of talking in total. Now why would you do this ? May be just for kicks.