If a Song Meter series recorder detects a problem with an SD card, it will mark the card as "Dirty" and no longer record to that card in order to avoid corrupting any further data.
This can happen if a recorder momentarily loses power or if the batteries drop below the voltage required to power the recorder.
If a Song Meter runs a recording schedule until the batteries are depleted, it is likely that the SD card(s) will be marked dirty at the end of the deployment. This is completely normal and should not cause alarm. There may also be empty .wav files at the end of a deployment when power is lost during recording.
On Windows (and other operating systems), when inserting a "dirty" card, the operating system should either automatically check and repair or prompt you to check and repair the card. This is almost always recoverable and your data should be preserved.
Dirty cards can be used again after they are formatted, either using the Format Cards utility on the Song Meter recorder, or by using theSD Association Formatter.