Hello HF

I collected some Info and I write this post, because i think this is a problem that occurs often in everyday life.

The iPhone battery is designed with longevity in mind, and it should retain up to 80 percent of its original capacity after 400 full charges, according to Apple. If your iPhone no longer holds a charge for the same length of time that it once did, you may need to invest in a replacement, but, if your battery simply refuses to charge, your problem is more likely related to your firmware or to an external factor. You can pinpoint the exact problem by doing a bit of troubleshooting.

Instructions

Things You'll Need:

iTunes
iPhone USB Cable

1- Leave the iPhone plugged in for several minutes. If the iPhone appears to not charge, at first, the battery may need time to restore before presenting any screen display. If the battery is completely dead, even a connected iPhone may remain unresponsive for a short time.

2- Connect your iPhone sync cable to a different USB slot. If you choose to charge your iPhone through a computer rather than through a wall outlet, make sure that you connect your cable to a port containing ample power. External USB hubs and keyboard USB ports often lack the power needed to charge an iPhone, so try to connect to a port directly on your computer.

3- Connect using a different USB cable. If your current iPhone USB cable contains a short circuit or other defect, it will not have the ability to transfer power from your computer or wall outlet to your iPhone. You can purchase a replacement USB sync cable from your local Apple Store and from many electronics stores.

4- Reset your iPhone. An inability to charge may indicate a frozen or malfunctioning operating system, which you can sometimes remedy with a hard reset. Hold down the two main buttons on your iPhone ("Home" and "Sleep/Wake") until the Apple icon appears.

5- Restore your iPhone after you have attempted every other troubleshooting method unsuccessfully. Use your sync cable to connect your iPhone to your PC or Mac, then open iTunes, select your iPhone from the "Devices" column and click on "Restore."

And IF your USB cable is damaged you can repair itself thus saving some money.
This is the scheme:

[IMG]http://img684.imageshack.us/img684/74/usbpinoutscheme.jpg[/IMG]

If you don't want to cut the iPhone cable, by an USB extension cord.
Make sure the positive and negative terminals are connected correctly and use a voltmeter to make sure everything is correct.

[IMG]http://img19.imageshack.us/img19/7523/usbpinout.jpg[/IMG]

I hope this was helpful for you my friends.

Thanks for reading...