Digital music player battery life is negatively impacted by playing digital rights-managed (DRM) files, a report explains.

The report points out that DRM poses an extra strain on the players, which must check that tracks are legitimate while they play them. This drains battery life. One of the worst offenders for this, according to CNet, are Windows Media-protected subscription music files.

The report points out that the Creative Zen Vision:M battery life falls to 12 from 16 hours when playing Napster-provided, Windows-protected subscription files.

Battery life is also impacted by using different headphones, playing music that has been compressed above 128k, leaving the screen lit, switching the music player on and off, playing music at high volume, watching video and images and so on.

The report warns that any battery life claims from manufacturers are only estimates. "Rated battery life should be used as a guide and never be taken literally," they write.