Originally Posted by rfog
Does Airplane mode disable the CDMA modem? Because I think the problem is there: the CDMA modem tries to connect and as I'm in Spain it uses all battery retrying connection
Yes. Putting on airplane mode will turn off your phone and wifi connection (your device will neither transmit nor attempt to receive) and will significantly improve your batter life. Really there is no reason not to be in airplane mode unless you are actively wanting to connect to the bookstore, or have just switched timezone and want to pick a new time signal.
It's not just a question of battery life for your convenience; most batteries have a fixed number of charge/discharge cycles, so the more you cycle them the sooner you will need a new one.
I certainly I am interested to know what your batter life is like reading 8-10 hours a day with airplane mode on. Though of course it does not strictly matter how many hours you read, but how many page turns you do.