Only the second time I notice this. With alkalines, I notice a white powder, almost fibrous filaments form on the terminal(s). I notice it once in an alarm clock, the power formed on both the terminals of the AA alkaline battery and the contacts of the alarm clock. The once more, I noticed this in a partially used AAA alkaline battery lying on a table for over a month. Simply wiping with a dry paper towel removes the powder. The battery is not leaking, as far as I know. What could this powder be?