I love my iPhone but as most people know, their battery life isn't the best.  I didn't want to buy a semi-permanent fixture to my phone to extend the battery life either.  I found the IMP500!  It is the perfect iPhone companion.  It is small enough to fit in my pocket or briefcase, it's capacity is large enough to charge my phone from almost being dead to full charge more than few times, and with its' USB port, I am also able to charge my bluetooth headset.  When you're done charging, you simply put it away!  One cable charges the device itself, then is used to charge your phone.  I love this thing so much that I don't leave the house without it.  I even got one for my brother-in-law for Christmas and now he tells all his friends about it too.  Trust me, THIS is the external battery you want for your iPhone.  Now I want to buy their external laptop battery.....