Here’s Fairphone’s spare part shop:
Bloating of a battery is something that is probably hard to avoid the older it gets and the heavier it has been used. If you buy a new battery, you can easily check it from time to time for early signs: Place it flat on a really flat surface and try to make it spin. If it’s easy to get it spinning, that’s a clear early sign for bloating.
By the way, here’s a topic appreciating holding on to a Fairphone for a long time: My FP3: 5 years and counting