All of a sudden this year my M100, which has been reliable, has super fast battery drain. Is there a hard reset of the camera or any software updates that would be able to correct this?
Doubt it will fix it, but worth a try. To do a hard reset, pull the battery tray out and there should be a little reset button just inside the camera. Before you hold the reset button down for a few seconds, let the camera set without the battery tray in it for about 15 minutes with the switch set to aim. This will drain any extra power left in the camera.
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