The documentation says 12V is the max tension recommended to power a Arduino Duemilanove, however the "limit" is 20V (see: http://www.arduino.cc/en/Main/ArduinoBoardDuemilanove).
Will the Arduino Duemilanove be OK if I power it with a 15V battery? I am using a shield on top of it, maybe it will be worse because of the heating?
Additionnal information: I will use the VIN pin to provide current to motors (up to 2A). I think there is no impact on the Arduino (because I will not draw power from the Arduino, but from the VIN that is directly connected to the battery), but I'm not sure of that.