There have been quite a few rumors going around regarding zune’s battery life. But this one is from a reliable source: zuneinsider.com.

After conducting the test they claim to have a battery life of up to 13 hrs, when listening to music, with the wireless turned off and up to 4 hrs of video or pictures. And up to 14 hrs when the wireless is turned off.

Somewhat surprising, now lets see under what circumstances the test was conducted. 128 kbps ripped WMA songs, played on repeat, backlight timer set to 1 sec, equalizer set to none, default volume setting and no other activities performed during the test not even browsing pictures.

So, the conditions under which the test was conducted are way below normal. Where as in the real world, there are ample of factors that will drain your battery much quicker than expected. Like for example browsing photos, switching tracks means hard disk in constant use, watching an occasional video and cranking the volume up and down.

Other than the factors mentioned above I stumbled upon an old article from mp3.com, which claim that the infamous DRM has a drastic effect on the battery life of any media player.

As per tests conducted by CNET, when playing WMA 10 DRM crippled subscription tracks, there is a loss of almost 4 hrs or up to 20 ~ 25% of playback time (Full article). So, heavy DRM not only slows down the player but eats up battery life too.

Taking all the above factors in to consideration, the battery life is going to be much lower than claimed.

Update: New zunes battery life tested.