Ipad battery issue

Hi there.

I've been using an M2 iPad Air, which has a maximum capacity of 100% and a cycle count of 18. I charged it to 80% on Monday. However, despite not using it, it lost 30% of its charge over the course of 4 days. I previously contacted Apple Support and turned off background processes, notifications, and so on, but the battery still drains quite fast.

Is this normal? Should I exchange it since I bought it from Costco and it's still refundable?