There is another interesting battery issue, mostly concerning those who still uses their M8 batteries in M9 cameras.
According to the M9 product specialist at Leica USA with whom I spoke the other day, older batteries that are reaching their end-of-life point (which is approximately two years) may cause an undercurrent situation. It makes a camera behave erratically leading to write errors, corrupted SD cards and camera acting like the battery is dead. I tend to believe him, because I used the M8 battery in all three instances of my M9 playing possum during high-pace shooting. This always happens when the battery has less than 30% charge.
