They might, but it's not recommended. Mechanical fit can be an issue, for example. It's mighty tight in there. Not all 18650s even fit, some that do are too long to allow the cap to be screwed fully down (which can cause contact problems, even damaging the spring loaded pin.
And it voids your warranty.
IMO you really only need at most one spare? I have one to support 3 (or 4?) Airs and very seldom use that one. Ten bucks to be sure, I think this is a bad time to get cheap? You can also get a 'power bank' to recharge as needed when away, which is also useful for other tasks? It is a USB chargeable device with a cheap cable you know like this:
https://www.amazon.com/gp/product/B00NQCMRJ6?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
Your call, but I have piles of 18650s from various projects around, like I said I bought a spare from PIU and recommend you do likewise. Well, OK, not necessarily from PIU but stick with the 'factory battery', one of the experts on such things, CentiZen, did a lot of testing and research and decided that exact 18650 was the best available for the duty and long life........Arizer made an educated Engineering decision, who'd have thought?
OF