1. The iPhone 5's battery is slightly less than a half an inch taller than the iPhone 4S. The thickness appears to be identical. UPDATE - Although, the thickness appears to be the same, the iPhone 5 battery is ever so slightly thinner. With an eye test, the iPhone 5 battery is maybe 1-2mm thinner.
2. The iPhone 5 is 3.8V/5.45Whr while the iPhone 4S is 3.7V/5.3Whr.
3. The connector on the iPhone 5 is not only different, it is placed on the opposite side of the battery to accomodiate its new position within the iPhone.
4. The iPhone 5 battery weighs approximately .80oz. The iPhone 4S battery is approximately .96oz
Apple has announced an event for September 12th at which it is expected to unveil the next generation iPhone.
Read More [via MacRumors]