The Intel MacBook Air battery was very easy to swap, just opening the bottom lid. Amazon has kits for about 40 bucks with the two necessary screwdrivers included.
Don't buy lithium-ion batteries on Amazon.
Especially not very large ones like in a laptop.
Just did this on a 2017 MacBook Air. Battery was cheap ($50?) and it was simple to do. Machine is working just fine now.
For what it's worth, if anyone comes back to read this, the battery just died :\