iPod classic 160gb modded to 256gb with 2000mah battery and Bluetooth. Just waiting on a 3d printed back. All fits within a thin shell. Very happy with how it's come up. :
iPod Classic new Battery & 256GB SD Card: still works in 2022! - YouTube
1 X 3000mah Ssd Hd Upgrade Battery For Ipod 5th Gen Video 30gb Ipod 6th Gen Classic 80gb 120gb 7th Gen 160gb + Repair Tools Kit - Mobile Phone Batteries - AliExpress