The rover will operate with a 273 W-hr battery pack to provide peak power as well as power when the rover's solar array is oriented away from the Sun. The pack is comprised of A123 lithium ion cells, which will be attached to one of the interior I-beams anchoring the radiator to the chassis. After designing and machining molds, the team laid up carbon composite materials over the molds this week to test production of the battery pack holder. In the photos, the cells are about the diameter of a U.S. quarter.