how can i protect my personal data while the battery is being replaced
will my personal data be protected when a technician replaces the battery in my MacBook air
MacBook Air 13″, macOS 10.15
Question marked as
If you are giving your Mac to an Apple Store yes. Apple has zero tolerance for employees who steal so much as a paperclip, let alone a customer's personal data.
Anyone else, who knows. If you want to be assured your data remains inaccessible then back up your Mac with Time Machine, then erase it. To learn how to use Time Machine please read Back up your files with Time Machine on Mac.
Presumably you already use FileVault: Encrypt Mac data with FileVault - Apple Support. If you do not, then by definition you are not concerned about having your Mac's data stolen.