Quote:
Originally Posted by sjfan
A micro SD card's sleep current is typically in the range of 0.2 mA drawn. If a Kindle with a typical 1420 mAH battery has 30 hours of continuous reading life, that's 47.333 mA of average draw; removing the SD card would decrease that to about 47.1 mA, saving you less than half a percent. Instead of 30 hours, you might get 30 hours and 7 minutes; it's not really going to be noticeable, and certainly isn't enough to impact how often you need to charge the battery.
All of these numbers are order-of-magnitude: maybe your SD card draws more like a 0.3 mA sleep current. But the basic story is the same: while there is a theoretical power draw there, there's not a big real-wold impact on reader battery lifespan (unlike with wifi or backlights, which can have a significant impact on battery life).
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The following is not about whether or not removing an SD card is a worthwhile battery conserving strategy, but an extension of the above very good start at estimating energy costs. The calculations below are mostly based on those above with 1 additional order-of-magnitude value, that 1 hour of continuous reading per day will deplete a fully charged battery in 15 days, approximately equivalent to a discharge in 30 days with no reading. This corresponds to a sleep current of about 2ma (2ma for 50% in 15 full days of sleeping, 2.087 for 15 days less 15 hours, I will go with the latter).
720mah/1.887ma = 381.558 hours or about 21.5 extra hours on a charge, not counting the 7 minutes during reading.