How difficult is it to replace a 2017 MacBook Air’s battery?

I highly recommend you have Apple or an Apple Authorized Service Provider replace the battery for you since this laptop is still fully supported by Apple. The quality of third party Lithium-ion batteries is extremely poor even when purchased from a reputable vendor.

The battery in a 2017 MBAir is relatively easy to replace, but care must be taken not to accidentally puncture the battery or damage the battery connector on the Logic Board....sometimes the battery can be hard to disconnect as the fit can be very tight. The battery in a 2017 MBAir is held in place with five Torx screws. This is the last Apple laptop with an easily replaceable battery which does not use adhesive. A 2018 MBAir also has a "removable" battery, but the adhesive is a pain to remove as you must pull the adhesive out without breaking the adhesive.

If you insist on a third party battery, then OWC is your best option (possibly iFixIt). OWC has instructional videos. While OWC normally has very good products, their batteries are not always as dependable as Apple's original batteries, but OWC and iFixIt batteries are the best of the third party ones. Even Apple has quality issues from time to time, so if Apple cannot guarantee getting 100% batteries, then none of the third parties has enough clout to ensure it either....in fact some third party batteries may be ones the OEM (aka Apple) decided was not good enough quality to meet their standards.

I personally will always choose an original OEM battery over any third party Lithium-ion battery. This is from someone who has been supporting our organization's thousands of laptops for over twenty years.

So difficult that you should let Apple do it. The battery is glued to the upper deck and requires solvents so dangerous that they should only be used by professionals. Wearing HAZMAT suites. Oh, and the solvers are extremely flammable.

You can use this service page to get an estimate of the cost:

Mac Repair & Service - Apple Support

Apple does not sell batteries as service parts, meaning you cannot buy an original. After-market batteries have proved to be awful compared to original nApple batteries, which you can only be assured of getting by letting Apple do the service.

The other issue is cost. Because of the glue situation, many independent service people can only replace the entire upper deck including frame, trackpad and keyboard. They will have to charge you 2-3X what Apple charges.

IHMO. you have one option. Apple.

we just changed a 2015 Air battery - it looks like an "H" and is glued to back shell. I chose to have a shop do it for me as I dont have those tools or eyesight anymore. 2017 may still be in coverage rage (2015 was antique range) so not sure if the battery and the aluminum back come as one piece or an easy change - it seemed to be priced that way when I asked an Apple Service depot last year.

It is surprisingly easy. It took me 10 minutes 8 months ago.

Apple in my region does not do it themselves. They use a third-party contractor who performs the change on-site for a total cost more than twice Apple’s cost for a newer machine. So I did it myself.