One feature I really feel is missing from the Arduino is the ability to plug in a LiPo battery directly - it requires 7-15V, making a 3.7V LiPo battery useless without a step-up converter.
And using USB power is a problem if you still want to be able to charge the device and code/read from it at the same time - The data inputs are not connected on most USB battery packs that charge from mini USB.
This is fine for hobbyists with direct access to all the electronics, but creates problems when the device is sealed in an enclosure.
A direct connection to the USB power lines instead of the 7-15V input would also solve the issue when using a seperate charging circuit/boost converter and while reading data.
Oh, and according to the website, 3.3V is only available while using USB power that flows through the FTDI chip, a problem when using 3.3V electronic and a 12V battery.
A charging circuit for a LiPo battery would really be lovely, since most chips are SMT and difficult to solder - I live in ZA and parts are not always readily available.
Everything is possible. But do you want 12V batteries or 3,7?
To use a LiPo, I'd guess that lowering the frequency and voltage in the Arduino to 3,3 would be the first step. Regarding the isolations and charging circuit, I'm not so sure since I haven't looked into it.
Have you looked at the SeeedStudio Arduino clones? They have the possibility to use batteries, although they still need to lower the frequency on the chip for it to be safe.
With this being said... the Maple board (and Olimexino "clone") already have the ability of using and charging LiPo batteries.
It includes charging and power-conversion for 3.7V LiPo batteries. As it stands it doesn't solve the problem of using USB for both charging and communication simultaneously, but I think conversion would be straightforward: you could desolder the 500mA fuse from an Uno, disconnecting the USB power from the Uno, and bring a wire from the exposed USB +5V pad to the +5V pin on the shield's charging connector.
Note the removed fuse, and the connection from the fuse's solder pad to the +V "charge" connection on the shield. The trace-cut and second wire are to allow the Uno's power-switching circuitry to work, and permit use of the dc power jack.
It's an ugly solution, and I agree there's a need for an Arduino board with integrated LiPo power circuitry. And since were talking about going wireless, such a board should also be able to use a solar panel to charge the battery. The Sparkfun charger is constant-current, making it unsuitable for the variable and unpredictable current that a solar panel supplies.
