The iPhone gets great battery life and the iPhone 6 Plus gets really great battery life. Apple has done a lot to make everything from their chipsets to their software management extremely power efficient. Yet every feature you use, you ultimately pay for with battery life. Most times it's not a problem.
If you start running low on power, you can simply plug into USB or an adapter and recharge really quickly. If you're going to be away from energy for a long period of time, however, there are a few tricks you can use to extend your battery life just a little bit longer. They'll cost you some fun and convenience, but they'll get you as far as you can possibly go.