1. I am not sure about iPhone, but on android phones you can turn off wi-fi, gps, bluetooth, etc. The less services are in use, the more is battery life. I am sure, if you put your phone in airplane mode, the battery will last longer.
Also the battery has a life time. This number depends on how the battery was used. Closer to the end the battery will hold less "juce". May be it is time to replace your batteries.