Hi,
Will this battery ( http://www.sparkfun.com/products/341 ) work with the Arduino Duemilanove?
Regards
Spec for the product is
Input Voltage (recommended) 7-12V
The regulator needs “headroom”, this being the difference between the AVR’s 5V requirement and the input voltage. At 7V in, the headroom is 2V.
So no, the 3.7V won’t work.
Beware too, how to charge those exotic-chemistry batteries safely.