Batteries are generally a cheap fix from third party stores. If you wanted to keep the phone why not spend the small dollars and just replace the battery?

Because you need to bring it to a shop, sometimes they may keep it for more times, sometimes if they are not that honest they will find something else and factory reset it and a long etc. If it's something one can do at home by one self as an expected and supported by the vendor operation, why not? You can still bring it to a store if you don't feel like crafty enough to do it.

Indeed, even directly from Apple a new battery is a whole lot less expensive than getting another phone.