The U.S. DOE Energy Efficiency and Renewable Energy (EERE) has a very informitive website for Alternative Fuels and Advanced Vehicles. The Vehicle Technologies Program Home Page is stocked full of information, images, and links. Below is an example of what you can find on the site. Check it out.
Hybrid Electric Vehicle Energy Storage Systems
An energy storage system is an essential component in hybrid electric vehicles (HEVs). Batteries used in HEVs should have high power (with high-peak and pulse-specific power), high specific energy at pulse power, high charge acceptance to maximize regenerative braking utilization, and long calendar and cycle life. See below to learn about HEV battery options, ultracapacitors (another energy storage device), and battery thermal management strategies.