If you don't like carrying a charger around with you, you'll probably be disappointed in the iPhone 6. The iPhone 5s and its puny 1,560 mAh battery lasted just 5 hours and 46 minutes on the Laptop Mag battery test, slightly below the 6-hour smartphone average and hours behind leaders like the 11-hour and 15-minute Galaxy Note 3. While it is possible that the iPhone 6 will include a higher-capacity battery than its predecessor, the latest rumors peg it with a much-larger 4.7 or 5.5-inch display (perhaps one model with each), which will undoubtedly consume more power.
If you're not happy with the iPhone 6's likely short battery life, you won't have many options. While Samsung's Galaxy phones and some LG handsets allow you to swap out your battery for a higher capacity unit or a backup of the same size, the iPhone 6 will probably ship with a Liquidmetal, unibody design that has a sealed back panel. You'll have to opt for a battery case if you want extra juice.