Apple announced last week that it intended to offer replacement batteries on iPhone 6 and higher models after being criticized for slowing down older phones. Apple said the slowing was to maintain performance on aging batteries, but the move was obviously not taken well by iPhone fans.
Originally, a new iPhone battery would set you back $79 from Apple, but with the new replacement program, they are available now for $29 no matter what condition your current battery is in.
If you have an iPhone 6 or later model, you can begin the replacement process online through Apple's website or you can visit an Apple Store.