Not car related but battery advice sought.

If you know your charger is good...... then this suggests the battery is either defective or too flat for the charger to recognise. Neither is great for a new battery so claiming warranty is probably the correct path.

However, if it’s “only” flat (and you should be able to establish this with a simple multimeter) you may be able to wake it up enough to get the charger to see it by applying something close to its rated voltage too it for a short while.

Nick