The signal

In 1970, a surgeon implanted a pacemaker powered by a 2.5-curie slug of plutonium-238 into a human chest. It worked. Over the decade that followed, Medtronic and its French partner Alcatel built and implanted around 139 of these atomic pacemakers, devices marketed on a single promise: this one you will never have to replace. Some of those patients are reportedly still alive, their hearts kept on rhythm by a sliver of isotope that has been decaying quietly since the Nixon administration (the history is documented in Medical Design & Outsourcing).

Then the idea died. Lithium-iodine cells arrived in the mid-1970s, lasted a good decade, and carried none of the paperwork or the dread of a radioactive implant. The last plutonium pacemaker went in around 1988. The radioisotope battery became a Cold War curiosity, filed next to the radium watch dial.

It is coming back. And the patent record shows it returning not from the national labs that kept the flame, but from a Florida startup, a Korean atomic-energy institute, an Australian two-man shop, and the single largest battery manufacturer on Earth.

The data

We track 9.3 million US patents. Granted American patents that actually describe a betavoltaic or radiovoltaic device, the technical name for a battery that converts radioactive beta decay straight into electricity, number 32 across the entire dataset. That is a tiny pile. But the shape of the pile is the story.

Through the late 2010s, these grants arrived at a rate of roughly one a year. The field was effectively dormant. Then the count moved: eight of the 32 have issued since the start of 2023, four of them in 2025 alone, with two more already granted in the first half of 2026. The most recent landed on May 12, 2026.

A doubling inside a near-dead category would be a footnote if the new names were the old names. They are not. The early grants belong to one cluster of American institutions: Cornell, its spinout Widetronix, the US Army, Lawrence Livermore, the University of Missouri. The new ones come from places that had nothing to do with this field a decade ago, on three continents, and one of them sells more batteries than anyone alive.

What a betavoltaic actually is

Run the coherence check before trusting the trend. Strip the word “betavoltaic” out of every one of these documents and read what is left, and they describe the same machine. A beta-emitting isotope, something that throws off electrons as it decays, sits against a semiconductor. The electrons slam into the semiconductor’s crystal lattice and knock loose electron-hole pairs, the same charge carriers a solar cell makes from photons. Wire it up and you get a trickle of direct current that does not stop until the isotope runs down, which for the right isotope means decades to centuries.

The engineering fight is always the same: pick an isotope energetic enough to be useful but benign enough to implant or ship, and find a semiconductor that survives its own power source. Read the recent claims and you watch a dozen teams attacking that problem from different angles.

City Labs in Miami builds its cells around tritium, a hydrogen isotope whose beta particles are so weak they cannot penetrate skin, sealed permanently inside a solid semiconductor. Its 2025 grant describes a power source small enough to ride inside a catheter and sit in vivo, charging a secondary cell to feed sensors or stimulators inside a living body. Korea’s atomic-energy institute, KAERI, patented a gallium-nitride cell whose p-type and n-type regions are written directly into the crystal with an ion beam, no etching, to expose more of the junction to the particle flux. A design matching Professor Su-il In’s group at Korea’s DGIST puts carbon-14, the isotope used in radiocarbon dating, on both electrodes of a dye-sensitized cell and routes the beta energy through a ruthenium dye that triggers what the team calls an electron avalanche, work In presented at the American Chemical Society and built on a 2020 paper in Chemical Communications. A Texas outfit called Direct Kinetic Solutions patented a way to pack tritium gas into the molecular cages of metal-organic frameworks, the porous sponges normally pitched for carbon capture, so the fuel sits right against the converter. Battelle’s version wraps scintillating particles in silica to catch beta energy that would otherwise escape and re-emit it as UV light a photodiode can harvest.

Different isotopes, different semiconductors, different geometries. Same physics, same goal: microwatts that flow for a human lifetime without a charging port. That is a technology, not a keyword.

Who’s building it

The volume leader is not a household name. City Labs holds roughly two dozen granted US patents covering tritium-to-electricity conversion and the packaging around it, a portfolio it has been compounding since 2014 while almost no one watched. The company took its first NIH award in 2019 to build a tritium battery for a leadless cardiac pacemaker, then a Commercialization Readiness award from the National Heart, Lung, and Blood Institute in 2024 to push toward pre-clinical testing. It is working with the German device maker BIOTRONIK on a leadless pacemaker meant to run for at least 20 years, against the roughly decade-long life of today’s leadless units from Medtronic and Boston Scientific. The pitch is almost word for word the 1970 pitch: a pacemaker you never replace. Tritium is the difference. It does not set off the alarms plutonium did.

Behind City Labs sits the old guard. Widetronix, spun out of Cornell’s Spencer Research Group in Ithaca on more than $2 million of Defense Department money, holds seven of these grants and originated the silicon-carbide-and-tritium design that converts about 30 percent of incoming beta particles to current. Cornell itself holds several more. Medtronic, the company that buried its own plutonium pacemaker in the 1980s, quietly took out two betavoltaic patents in 2015.

Then there is the name that does not fit. Contemporary Amperex Technology, CATL, makes more than a third of the world’s electric-vehicle batteries. In July 2025 it was granted a US patent for a perovskite betavoltaic-photovoltaic battery, a cell whose perovskite layer, the same family of materials CATL has been pushing for cheap solar, is doped with a fluorescent substance so it can harvest both beta particles and the light they generate. A second CATL radioisotope-battery grant issued in 2023. When the company with the planet’s largest wet-chemistry battery manufacturing base files patents on a nuclear micro-cell, the relevant fact is not the patent. It is the factory behind it.

Who cares

Nobody is going to run a phone on one of these. The output is measured in microwatts; the BV100 cell that China’s Betavolt put into what it called mass production in January 2024, a nickel-63 source sandwiched between two diamond semiconductor wafers in a package smaller than a coin, makes 100 microwatts and is rated for 50 years (Live Science, Tom’s Hardware). That is roughly a millionth of what a phone draws. It is also exactly enough for the things you can never reach to recharge: a pacemaker in a chest, a sensor on the seafloor, a node on a spacecraft past Jupiter, an implant threaded into a nerve.

That is the market the patents are circling, the one corner of electronics where “lasts longer than everything around it” beats power density. The strategic read is in the geography. China has a company claiming a production line and a roadmap to a one-watt cell. The United States has a Miami startup with NIH money and a 12-year patent lead but no product yet cleared for a human. Korea has its national atomic institute. Australia and Texas have two-person teams. The isotope that scared regulators out of the room in 1988 has been swapped for tritium and carbon-14, sealed in solid state, and the door that closed forty years ago is open again.

The most telling detail is the borrowed tricks. The perovskite came from solar. The metal-organic framework came from carbon capture. The dye-sensitized electrode came from a different solar cell entirely. Three techniques perfected in neighboring fields, all now pointed at the oldest unsolved problem in implant power. The nuclear battery did not get reinvented. It got surrounded.

Method note. Counts come from a corpus of 9.3 million US utility grants sourced from USPTO bulk grant XML, searched for full-text mentions of “betavoltaic” and “radiovoltaic” and de-duplicated to distinct documents; the 32-grant figure and the year-by-year trend reflect that exact filter, so devices described only as “radioisotope” or “nuclear” batteries without the betavoltaic term sit outside it. Assignee tallies combine variant corporate spellings and were confirmed against published patent records; several 2025–2026 grants carry no assignee in the bulk feed and were attributed by reading the published patent (City Labs, KAERI, Direct Kinetic Solutions, GenX Energy of Australia). Patent claims and abstracts were read directly. Company, funding, and product details are drawn from City Labs, the Cornell Chronicle, MIT Technology Review, the American Chemical Society, Live Science, Tom’s Hardware, and Medical Design & Outsourcing, cited inline. No clinical claims are made here: the medical devices described are pre-clinical, and nothing in this brief should be read as a statement about patient outcomes.