You should have no trouble running a piece of equipment which takes AAA batteries on other size batteries, as long as they are electrically connected in the same way and the batteries have the same voltage as the AAA ones you are replacing. Check the wiring (or in the case of battery clips, the configuration of the metal clips), but I'll bet the two AAA's are wired up in series. Each standard AAA battery provides 1.5 Volts, and so any two 1.5 volt batteries wired up in series will do the job. You can even use two C or D batteries if you like. Other common batteries put out 6, 9, and 12 volts -- these cannot be used.
The biggest concern then is just getting the batteries to fit where you want to put them. MP3 players are really small, which is why they went for the AAA batteries in the first place. You might be able to get pre-made battery holders with the metal springs and clips already wired up from an electronics supply store.
Tom
(published on 10/22/2007)
