from
http://hbpiper.wikispaces.com/Nuclear+Power?f=print

3. Power Cartridges
Power cartridges (also called nuclear-electric conversion units) were small things that seem to have replaced the battery and all small engines in the Terran Federation. They were collapsium coated metal cylinders which yielded substantial amounts of power with 100% efficiency — no waste heat worth mentioning. They got their energy — somehow — from radioactive materials (reactor waste, probably) stored in them. They lasted for years. It seems likely that contra gravity vehicles were powered by larger power cartridges.

[Quote from Junkyard Planet about how they're made...]

The power cartridge manufacturing plant “was built in the shape of a T. One side of the cross-stroke contained the cartridge-case plant, where presses formed sheet-steel cylinders, some as small as a round of pistol ammunition and some the size of ten-gallon kegs. They moved toward the center on a production line, finally reaching a matter-collapser where they were plated with collapsium. From the other side, radioactive isotopes, mostly reactor-waste, came in through evacuated and collapsium-shielded chambers, were sorted, and finally, where the cross-arm of the T joined the downstroke, packed in the collapsium cases. The production line continued at right angles down the long building in which the apparatus which converted nuclear energy to electric current was assembled and packed; at the end, the finished power cartridges came off, big ones for heavy machines and tiny ones for things like hand tools and pocket lighters and razors. There were stacks of them, in all sizes, loaded on skids and ready to move out. Except for the minute and unavoidable leakage of current, they were as good as the day they were assembled, and would be for another century.” [Junkyard Planet]

from “Omnilingual”
“They all got out of the truck and stretched their legs and looked up the road to the tall building with the queer conical cap askew on its top. The four little figures that had been busy against its wall climbed into the jeep and started back slowly, the smallest of them, Sachiko Koremitsu, paying out an electric cable behind. When it pulled up beside the truck, they climbed out; Sachiko attached the free end of the cable to a nuclear-electric battery. At once, dirty gray smoke and orange dust puffed out from the wall of the building, and, a second later, the multiple explosion banged.”

He talks about more about how they work and are manufactured in “The Cosmic Computer” AKA “Junkyard Planet”