How much do you think i could squeeze out a lith-ion?
Li-po/ion don't come in standard mah sizes, you buy the capacity you need. They also are wired in series strings of 3.7volt per cell nominal voltage, so you would need a 2 or 3 cell pack to wire to the external power plug of an Arduino. I use a small 2 cell li-po from a cheap R/C helicoper. Again any real meaningful battery life requires calculation once you know the actual current consumtion and have determined what you want for discharge time.
Lefty