BTW, FLAC is computationally simple to decode (compared to lossy formats), so it might even have a positive effect on run time. Although most people probably won’t want to sacrifice the required storage space for a little longer run time.
Most modern architectures run memory at a different (and usually much lower) clock speed than the processor, even when the memory controller is on-die and technically able to run synchronously. This is the reason why, for example, lookup tables are generally less efficient these days than just recalculating values: performance is mostly dominated by how fast you can fetch from RAM, not how fast you ALUs crunch math and logic operations.
FLAC is definitely computationally cheap to decode, but as sansafix confirms, I/O is the biggest power draw. Decoding one second of audio requires far more compressed bits to be copied from flash storage to work RAM if you’re using FLAC than Vorbis or MP3. Even a format with computationally heavy decode requirements would mostly draw power because of the number of RAM reads and writes than how much actual number crunching is performed.
(as an aside, the storage and battery tradeoffs still don’t offset the huge convenience of being able to play archival-quality FLAC files without having to transcode during the copy-to-the-player phase. Bravo, SanDisk, and thanks)