For most of us, recharging a phone is simply a matter of finding a standard electrical outlet.

But war zones aren’t so conveniently wired. As the military learned during more than a decade at war, supplying immense quantities of diesel fuel for generators at forward operating bases proved costly in money and lives.

To keep their radios and sensors powered up, some soldiers in Afghanistan lug almost 30 pounds of batteries during long patrols. During the summer heat, the added weight can contribute to potentially lethal heat exhaustion.

Faced with its staggering power demands, the Pentagon is turning to the most potent and portable energy source there is—nuclear energy—to keep its soldiers supplied with juice.

A 2013 report by the Defense Science Board identified “nuclear batteries” as an essential technology for the U.S. military in the 21st century. Though the technology sounds like science fiction, nuclear batteries have long served space exploration and medicine.

The technology exists. The problem is how to dispose of the batteries without contaminating the environment.