Just completed the first revision of a power board I’ve been working on for Gadgeteer.
It has three power sources: DC jack, mini-USB and Li-Pol battery, and will automatically switch between them.
It also has D and U connections. The D allows you to power and program your Gadgeteer device. The U connection is a serial port that sends a NEMA like string with system state data such as power source in use, battery charge, percentage etc.