What capacity SD cards can be used and what's the file partition format used?

The SD card needs to be formatted to the primary FAT32 MBR partition type.

Polyend Tracker is offered with a 16 GB microSD card, larger SD cards can also be used as long as they are correctly formatted (The built-in disk-utility under Mac OS will allow you to select FAT32 for formatting).
We recommend UHS-I cards / U3 cards.