How many lithium-ion batteries does a M1 MacBook Air (2020) have?
The answer is zero batteries in the adapter and the assembled laptop qualifies as UN 3481 product for shipping purposes.

The M1 Air has a built-in 49.9‑watt‑hour lithium‑polymer battery, so it falls under UN 3481, Section II IMP:ELI

To elaborate, you are shipping a computer (portable electronic equipment) that contains one battery with multiple cells and this assembly is regulated differently than loose batteries included in a box (or spare parts for repair of an Air).
Here is the relevant section from a 30 page guide from UPS.  Ask your carrier how they define portable electronic equipment if you are not sure if the shipping standard I have quoted doesn’t govern EMS website or staff.

https://www.ups.com/media/en/lithium_batteries_guidance.pdf