From DARPA:

The teams using the DARPA-developed Atlas robot got their first look at the newly upgraded system during a technical shakeout the week of January 12th in Waltham, Mass. The upgraded Atlas is 75 percent new—only the lower legs and feet were carried over from the original design. Lighter materials allowed for inclusion of a battery and a new pump system with only a modest increase in overall weight; the upgraded robot is 6-foot-2 (1.88 meters) and weighs 345 pounds (156.5 kilograms).

The most significant changes are to the robot’s power supply and pump. Atlas will now carry an onboard 3.7-kilowatt-hour lithium-ion battery pack, with the potential for one hour of “mixed mission” operation that includes walking, standing, use of tools, and other movements. This will drive a new variable-pressure pump that allows for more efficient operation... (full details)