International Battery bought machines from China that manufacture the components and has been tweaking them to make them run faster, use fewer materials and produce a better product. Each button on the control panels is labeled in Chinese characters, with English penciled in by hand underneath. Near Mr. Peters’s machine, a cardboard box awaiting unpacking bears hand lettering that says, “Glass Please Carefully.”

Other companies are also trying out new chemistries and materials, at the positive and negative terminals of the battery. As technicians try to improve battery assembly, the first requirement is a strikingly clean work environment. Mr. Peters, in goggles and spotless rubber gloves, declined to shake hands recently, just as a surgeon might on the way into the operator room.

The gloves protect him from the chemicals in the battery, which include nickel, cobalt and manganese, and shield the battery’s delicate tissues from the natural oils on his fingers.

“We don’t want any debris,” said Mr. Peters, who formerly worked at a nearby factory that made bulletproof glass. (International Battery’s pristine new showplace was previously an appliance repair shop.)

The engineers face a difficult challenge. The batteries have to store a lot of energy in a small, light package, scoring high in a quality known as energy density. They also have to absorb energy and give it back quickly, a factor called power density.

Think of a battery as a bottle for energy, and the power density as the size of the bottle’s neck. Good power density means a shape like a peanut butter jar, easy to fill or empty; low power density is more like a wine jug with a narrow neck.

The batteries have to charge quickly and withstand thousands of cycles of charge and discharge. They have to dissipate heat without catching fire, a product problem that a giant like Apple Computer could survive but a start-up electric car company probably could not. The batteries must function in Maine winters and Texas summers.