Like its predecessor, the Tegra 3, NVIDIA's Tegra 4, like its predecessor, is a quad-core processor along with a "hidden" or "stealth" fifth low-power core used save battery life. The fifth core is used during tasks like checking emails, performing notifications, running the operating system in sleep mode, and keeping the system alive when you are reading a book, playing media files, and so forth. None of these tasks don't require a high-powered CPU to run.
The system is known as a 4-plus-1 setup, but while that battery-saving system is held over from the Tegra 3, the Tegra 4 is built on an entirely-new architecture. According to NVIDIA's CEO Jen-Hsun Huang, the Tegra 4 is the world's fastest mobile processor, faster than anything currently on the market (yes, he's talking about you, Apple's A6X).
In addition, it's rumored that the fourth-generation Tegra is produced using a new 28nm manufacturing process, which would be a step up from the Tegra 3's 40nm process, and should help improve battery life despite the Tegra 4's increased processor power.
The Tegra 4 is going to need that new 28nm process to improve battery life -- assuming it exists. One of the reasons that the Tegra 3 fell behind Qualcomm's Snapdragon in terms of device use was because of poor battery life. Unlike the Qualcomm chipset, the Tegra 3 did not have an integrated LTE chip, which negatively impacted battery life in comparison.
Unfortunately, the Tegra 4 once again lacks built-in LTE support, which may again negatively affect battery life. Notably, the latest quad-core Snapdragon chipsets don't integrate LTE either, but Qualcomm is expected fix that issue something in the spring, while most believe that NVIDIA is unlikely to do so until later in the year, meaning it may fall behind yet again.