Neither is technically user replaceable but the MBA makes it easier. The MacBook Pro is glued in while the MacBook Air apparently has pull tabs. It is still very involved and requires removal of a bunch of parts including the main circuit board.
On ifixit.com it is something like 85 steps to replace the battery on the 13" MacBook Pro with Touch Bar vs. 45 steps for the 2020 MacBook Air. With the Air, you don't need adhesive remover, with the Pro you do. I personally wouldn't want to try and replace the battery in either of them. Too many small and fragile parts.Glued in place is a little misleading as its just strong adhesive, but if its anything like the other 13" MBPs it's really not that involved. I recently removed the battery on my 2014 Pro to replace the trackpad.
1. Remove the back panel
2. Disconnect the battery
3. Unscrew the speakers and move them out of the way.
4. Put a couple of drops of acetone under the battery cells so often the adhesive.
5. Cut the adhesive with plastic cards
6. Remove the battery.
That being said, hopefully the new Pro uses the same adhesive with pull tabs that the Air does.
On ifixit.com it is something like 85 steps to replace the battery on the 13" MacBook Pro with Touch Bar vs. 45 steps for the 2020 MacBook Air. With the Air, you don't need adhesive remover, with the Pro you do. I personally wouldn't want to try and replace the battery in either of them. Too many small and fragile parts.
Thanks - 3-5 years is realistic for me. I dont keep tech older than 5years*@Leon1das - how long do you typically keep your laptops, and how many times in the past have you felt it necessary to replace batteries? Just curious since I've not typically needed to do so, but I typically replace the computer within 3-5 years.
IMHO there are other factors to drive deciding whether MBA or MBP is the better fit to your needs than whether battery replacement might cost more with one than the other if you should ever need to do so.
Apple provides fixed-fee out-of-warranty battery services, at least in the US. See Mac Repair - Official Apple Support
MBP is more expensive than MBA, but both are fairly reasonable when you also consider the work is warranted and that the price of the actual OEM battery from known reputable shops. Don't wanna play battery-roulette with a 58watt-hour battery... Not to mention no worries about screwing up the replacement and trashing your computer.