Just in case: Swollen batteries are dangerous, it is strongly recommended to stop using batteries when you notice that they’re swelling. Also, if you have a Fairphone 1U that is less than 2 years old, this is likely covered under warranty. (If you have an FP2 it will also be a warranty case). See the full information, including warnings about the dangers of swollen batteries and comments on battery warranty, on the Fairphone support pages here.
Edit: also, some parts may not be available for purchase in lager quantities (see here).