In the race to power the next generation of medical devices, engineers have increasingly turned to advanced electrochemical cells. One of the most promising areas is the miniaturization of lithium-ion batteries for use in pacemakers, neural stimulators, and drug delivery systems. These batteries rely on controlled redox reactions, where lithium ions are transferred from anode to cathode through a non-aqueous electrolyte, releasing energy used to drive biological support functions.

Figure 1Schematic of a pacemaker battery.

Figure 1 illustrates the internal structure of a typical pacemaker battery. Understanding this internal configuration is critical when evaluating how energy is delivered to surrounding circuitry and biological tissues.

To ensure patient safety and device longevity, these systems must regulate internal resistance and prevent overcharging, which can lead to short circuits and thermal runaway. One way to characterize battery behavior under realistic operating conditions is by examining how load voltage responds to different current drains, as shown in Figure 2.

Figure 2Typical load voltage versus current drain plot for a pacemaker battery.

As Figure 2 shows, the voltage delivered by the battery decreases non-linearly as current demand increases. This characteristic must be considered in both the design and long-term calibration of power-sensitive implants.

Researchers are also investigating the role of magnetic shielding in these compact devices, as external magnetic fields—such as those from MRI scanners—can interfere with internal circuits, potentially inducing unwanted currents via electromagnetic induction.

Faraday’s law of induction governs the behavior of these currents. If a time-varying magnetic field penetrates a closed conducting loop, an electromotive force (emf) is induced. The magnitude of the induced emf depends on the rate of change of magnetic flux through the loop. In real-world applications, such as wireless charging of implanted devices, careful alignment of external and internal coils is required to optimize power transfer while minimizing tissue heating.

While electrochemical reactions are governed by changes in Gibbs free energy, the electrical work performed by induced currents is dictated by physical laws from electromagnetism. Bridging these domains is essential to safely deploy such medical technologies.