With great surprise, I realized that the battery lasts longer and longer. It may be partly due to loss of novelty, though I don't think I fiddle with the phone much less than at the beginning. Other than that, there's no explanation.
At the beginning, it took several hours to exhaust the battery completely. Now, it is quite normal for the battery to last two days, with both network and sattelite GPS, and WiFi turned on.
<start your conspiracy theories here>