The battery life stated in the specifications on the MP3/MP4 player is based generally on the runtime from a full charge in ideal conditions.
A number of tests are run for the battery life using songs encoded in various formats (including MP3, WMA and OGG), based on the following conditions:
• The songs are played continuously through a playlist without interruption
• Backlight display is set to go off within a few seconds
• Volume set to about 50 to 75 percent
• All music has a bit rate of 128kbps
• Equalizer is set to off, using factory default settings
The battery life is dependent on the format and bit rate of file that is played. If large or uncompressed audio files (including AIFF or WAV format) are played, more power is required by the decoder in the process of decoding the song. Hence the duration of the battery life will be shorter.
For example, Microsoft’s Window Media Audio (WMA) which is more complex than MP3 causes the processor to use more power in the process of decoding the file. Therefore, more battery power is required and the battery life is shorter. The power consumption is higher in the case of decoding the file with a higher bit rate, due to substantial improvement in sound quality and higher level of compressing, even if the file are in the same format but different bit rate will cause a difference in the battery life.
It is adviable to compress them or use a different compression method such as MP3, when importing them into your MP3/MP4 player. You can also consider breaking very long songs or tracks into shorter tracks that have smaller file sizes. If you encode your music at 128 Kbps, your MP3/MP4 player will fill its cache about every 25 minutes and hence it will enable the battery to last longer.