Yes ... its called "The Apple sales cycle" .. joking aside, before I get a new phone I check out the iFixit repairability score as some units that seem like they are not replaceable can be replaced pretty easily (like my Wife's iphone 5)

99% of batteries can be replaced in a phone IME. There are very few that are actually made at the same factory as the phone itself so theres no real barrier to removing and putting a new one in yourself as such. How do you think they get into the phone to start with ? ;)

Might have to cut a wire, but long as youre comfortable reconnecting it to the new battery, you should be all good. This is all IME, youre mileage may vary :)