Rechargeable lipo battery over USB

That's what's needed - by switching to a lipo battery, the entire device footprint can be almost halved! First thoughts were of a 7.4v lipo (double-cell battery) but the Nokia shield has already proved that a simple dc-to-dc step up converter can do the job where supply voltage is lower than the required voltage.

Charging requirements for lipo (or li-ion polymer) batteries are very specific and charging more than one cell can be quite tricky - particularly because of the need to stay within safety limits during charging.

It would probably be much easier/safer to stick to a single 3.7v battery with integrated USB charging circuit, and use this to power the Score Sure range of devices.
From initial investigations, a single battery would be much simpler to work with.
In fact, a recent email from NuElectronics confirms that they are working on developing this very idea themselves, to allow roboteers to power Arduino boards (which require 5v) from a single 3.7v lipo cell.

Charging circuits for single cells are freely available on the net and use relatively simple and inexpensive components.
At the heart of most chargers is the MCP73861 by Microchip.

More details (and schematics) will be posted here as they become available....