The provided 12volt charger has an adapter to plug in the 12volt socket in the boot NOT. The cigarette lighter socket. That power shuts down when the car is off.

Under the hood. Attach red clip to red terminal on battery, Black on grounding nut.

If using eyelet adapters, loosen nuts on battery, slide eyelets over corresponding color over corresponding terminal and replace nuts to secure. This is more permanent solution . Just disconnect cable at connector when done and leave the short cable attached and in the engine bay.

It's already wired under the hood with eyelets and I charged it to 100%, and I still get the " battery not charged" message

Does the engine start?
did you push the connectors tight so that the two cables snap together ?

The engine starts fine. Drives without any problem.

The connectors were tight. The green light showing full charge was in after an overnight charge.

Could it be a faulty alternator? I mean the car is brand new. It's baffling.

Straight back to the dealer if I were you. I’m sure it’s something minor.

I eventually figured it out.

I did a second charge using the cigarette adapter through the trunk. It appeared to reset the battery warning.

All is running well.