When Apple introduced the second-generation iPod touch in 2008, it promised 36 hours of run time when playing back audio and doing nothing else—a claim both it and its 2009 third-generation sequel surpassed by nearly four hours. They used 2.92 Watt-Hour batteries at 3.7 volts, or roughly 789mAh.
The fourth-generation iPod touch has just been revealed in photographs inside and out by the FCC, and surprise, there’s a 3.44 Watt-Hour battery in there at the same 3.7 Volts, or roughly 930mAh. This year, Apple’s promising 40 hours of audio run time, though the math would suggest the iPod touch battery should surpass that if everything else was being held equal—42 hours at a minimum for audio, 46 hours more likely.
Realistically, however, there are other factors that go into determining a battery’s life: the power drained by the new screen and cameras could be greater, the A4 chip might or might not be gulping more power than the prior iPod touch processors, and so on. We’ll have to see when the iPod touch arrives how it actually does in longevity testing. Earlier models have had wicked standby time—weeks if not longer—but really wore down quickly with certain processor-intensive games. FaceTime and video recording are even more demanding, typically. Expect some concrete numbers soon.