There are a number of backup batteries you can get for your iPhone to help extend the life between charges. These types of batteries aren’t ones you change with your regular battery, instead you connect them via a USB connection. The best backup batteries are rechargeable and depending on what type you buy you might be able to recharge it with a wall charger, car charger, solar power and some even have a hand crank although they can be inconvenient. You can find backup batteries for you iPhone at stores such as Best Buy or online through Amazon.