prosper50:
My apologies, I was simply abbreviating duemilanove.No, it is a plastic work surface, and the battery has been sitting in my desk drawer for at least a week (so not fresh off the charger).
So what measurements have you taken with a digital multimeter? If you truly want to solve this 'mystery' then you need to make a series of voltage and current reading while that battery is wired to the arduino.
Lefty