From pacemakers to neurostimulators, implantable medical devices rely on batteries to keep the heart on beat and dampen pain. But batteries eventually run low and require invasive surgeries to replace. To address these challenges, researchers in China devised an implantable battery that runs on oxygen in the body. The study, published March 27 in the journal Chem, shows in rats that the proof-of-concept design can deliver stable power and is compatible with the biological system.