CrossRoads:
A Large coin cell battery has these characterics:
Rated Voltage 3V
Capacity 225mAhNot going to last very long driving an SD card.
"new 328P chips come programmed with the INTERNAL 8 mhz oscillator enabled,"
is divide by 8 also enabled by default, so it would run at 1 MHz?
Lithium coin cells are usually 3.6 volts, not 3.0.
And a question: Does an SD card ALWAYS draw "full" current (even when chip select is not asserted)?
I would think you would select the SD card, read or write the data, then put it back to sleep.
There's no reason I can think of for any flash memory card to ALWAYS draw full current.