Battery: 2600mAh to give extra battery life and thickness to TG01
Battery cover: comes attached with a stock-like microUSB slot cover. User has to cut and remove the original slot cover to use it.
A flex cable inside the new slot cover connects it to the circuitry inside the battery cover.
The new battery cover relocates the microUSB connector to the bottom of the battery cover, and adds a 3.5" audio jack at the bottom of the battery. At the right of the battery cover (on the side of the up/down buttons) is a SD card reader, connected to the device's USB host pins, which is only activated when a SD card is inserted. (like the card readers found on notebooks)
If there is sufficient free space, add an extra USB port. A half-height USB port can be used instead of a standard sized one.
This shouldn't be impossible to make, just think of all those 3-in-1 adapters (charge, sync, audio out) for HTC devices, but in the form of a battery cover. The SD card reader and USB port activation/deactivation can be done with a switch.
With this addon, we make our device a very nice, portable, multifunction device.