Hello! The newer models of the Xiaomi Mi Notebook Pro (released in 2019 and later) have reportedly fixed the issue with grinding fans that was present in some earlier models. As for the battery, it has been reported to have a good lifespan and performance. However, like any battery, it will degrade over time and with use.
Regarding the AU adapter, you can purchase one from most electronics stores or online retailers that sell adapters and converters. Just make sure to check the voltage and current specifications of the adapter to ensure it is compatible with the Mi Notebook Pro.