This is how my iPhone 3GS looks like when it’s charging.
To have your phone charging screen looking like this, you must first have your phone jail broken with Winterboard installed.

Then download the theme file here and follow the instructions contained within it.

As of July 25 2010, thanks to the gracious hosting from Planet-iPhones, you can now download the Bracercom Battery theme directly from Cydia.
Just search for “Bracercom Battery” in Cydia and you will have it.

As of 12 December 2010, the HD Version of the Bracercom Battery theme for iPhone 4’s retina display is available in Cydia, thanks once again to Planet-iPhones for hosting it.