Can the battery in a Moto G4 (NOT Plus…play…etc) be changed? If so, what is the part number?
I would point out if this is more than a question of curiosity, your Moto G4 remains under manufacturer’s warranty. If the battery is truly in need of replacement now; it should be covered.
It is not meant to be a consumer-swappable battery. Experienced DIY’ers might try using the guide @drm186 posted, others might find a repair shop to do the work, and, as @rolandh suggested, if the battery fails due to a manufacturer’s defect during the first year of ownership, it would be covered under warranty. If you’re specifically looking for a phone that lets you keep a spare battery on hand and swap out halfway through a long, busy day, the Moto G (4th Gen) is not the phone you need.