Help with making aux. 5V battery pack

[IronHorseDriver]

Hello folks,
  It's been years since I've designed any electronic circuits (I graduated from HS electronics 25 years ago), so I'm a bit rusty in this realm.  I want to make a simple auxiliary battery pack, that can use 4 AA batteries, to run an MP3 player after the internal battery runs down (I am going on a long overseas flight and the flight duration is much longer than the battery life of the MP3 player).
  Trouble is, the output of 4 AA batteries is 6 volts, and the input voltage of the MP3 player (a Cowon iAudio X5) is only 5V.  I'm not sure whether the 1V difference will cause a problem, and I already e-mailed Cowon Technical Support to enquire about this.  I know I can use NiCads, which have a 1.2V output, but I have a bunch of fresh alkalines at home and would prefer to use them.
  I was thinking (mind you, it's been quite a while) of placing a 5.0V zener diode across the output, but I think that this will cause a constant drain on the battteries.  Is there a better solution?  Preferably, one that will not cost a lot of money in components, and with the parts available from Radio Shack.
  Additionally, if anyone knows of electronic component supply outlets in the Chicagoland area, kindly advise me.
  If anyone can provide assistance and/or e-mail me a rough circuit diagram I would be most grateful.

Sean

[audioguru]

Hi Sean,
Welcome to our forum.
DON'T put a 5V zener diode across your 6V battery. It current will be infinite and blow the zener and kill the battery very quickly.
Connect a 1N4001 diode in series with one of the battery's wires, the right way around, and its output voltage with new battery cells will be 5.3V which will be fine.

An alkaline battery cell drops quickly to about 1.25V (5V for four) so the voltage after the added diode will be only 4.3V for most of their life. Therefore I recommend that you use Energizer's new Lithium AA cells which have a voltage that stays at 1.4V (5.6V for four) for most of their much longer life. They cost a little more than alkalines. They are lighter weight too.

[Ldanielrosa]

A low dropout voltage regulator should do the trick.  They often have a very low quiescent curent.

Depending on some details pertaining to your email address, you may be able to get free samples from Microchip.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=64

Look under analog & interface products.

If you are not disqualified due to a bulk email address, you should be able to get some goodies within a week.