There is an internal uSD card holder that has a card in it for the system and a user area.
You can replace the 4GB card it comes with, with a larger one. The external uSD card, at the bottom, is not part of this and normally has no system partition, no firmware.
If you want to try disconnecting the battery, use a toothpick to probe around the connector and see which way it disconnects. As I remember it, it was straight up.
Luck;
Ken