On most models (especially the original 3DS and 3DS XL), a duplicate white serial number sticker is affixed to the motherboard housing inside the battery compartment. You will need a small Phillips #00 screwdriver to remove the battery cover.
Remove the screws securing the bottom housing or battery door. Lift the cover away to expose the battery compartment. Nintendo 3ds Serial Number Lookup
To help narrow down your search or determine your console's history, let me know: What are the of your serial number? What color or special edition branding does the shell have? On most models (especially the original 3DS and
If your console's external sticker says QW (North American New 3DS XL) but the sticker under the battery cover reads QJ (Japanese), the console has been reshelled or altered. 4. Repairs and Parts Matching Lift the cover away to expose the battery compartment