You can have the power (when you need it most)

King Richard trying to bargain
for a horse, early on when he was
offering just this "jewel-encrusted,
gold and steel sword that holds
an edge like a Ginsu knife."

It's the horror of the mini-electronics age: your mobile phone dies just when you're boss is supposed to be calling, or your MP3 player dies halfway through "Stairway to Heaven. "

"Five volts DC! Five volts DC! My kingdom for five volts DC!"  to update a line from Richard III, who lived when power was just as essential, but came primarily from horses, not rechargeable batteries.

Well, save your kingdom and, instead, get a rechargeable five volt USB power pack, like this little gem from Sanyo.

It's basically a rechargeable lithium-ion battery. What makes it nice is that it's versatile, convenient and compact.  When your device dies, you just hook it to the power pack.  You're instantly back in action, and, after a bit, your device will be recharged and ready to go it alone again.

The power packs are convenient because they take advantage of the increasingly standard USB power.

One end is the charging end: it has a mini USB jack and a jack for the power supply that comes with it.  You can charge it up either by connecting it to the power supply which plugs into the wall, or by connecting it to any USB power source, like the one ones on your computer.

Once it's charged, you carry it around with you waiting to use the other end, the supply end.

On this end there are two USB jacks.  These supply the power for your dead device(s).

For anything that charges from a mini USB plug, you can use the cable that comes with it.  For the increasing number of devices that charge from micro USB, you can either carry a separate cable, or get a mini-to-micro adapter like the one from Radio Shack.  (It costs $14, but the cheaper ones I've found online come to the same price or more when you add shipping).

If your device has a special jack, like the Sansa Fuze I carry everywhere, you have to carry that cable, too.

Yes, your minuscule mobile phone will be bigger with the power pack attached.  And, if anyone notices, it can look a little geeky.  But not nearly as bad as those people you see sprawled on the floor trying to use their phones while they're plugged in under a row of chairs at the airport.

With a little effort, you can make the connection almost invisible.  A cable running from your pocket to your device isn't much more intrusive then a headphone cord.  If you're just waiting for a all, you can just leave the whole ball of wax in your pocket, purse or brief case.

There are a bunch of brands out there.  The one I have is the Sanyo KBC-L2.  I've been using it quite a bit for about six months and haven't had any problems.

Technical Specs
Each of the output USB jacks supply 5.0V at 500mA.  That's the standard USB spec, so it should work fine for most devices.  Some phones push the limits by using USB, but drawing up to an amp.  The only thing I've noticed with them is that they'll operate, but won't pick up any charge.

When it's charging, the pack uses 5V and draws from 500mA from the USB jack or 1A from the AC wall charger.

Incidentally, I abandoned the wall charger immediately.  It's a lot more convenient to carry a universal USB wall charger.  In fact, I was just a little irritated that Sanyo included a generic charger rather than a universal USB wall charger.

When I get around to it, I'll chop off the plug that came with the wall charger and replace it with a USB jack (or plug).