Modern pacemakers run on a small lithium-iodine battery sealed inside the device’s titanium case. This chemistry has been the standard power source for cardiac pacemakers since the early 1970s, and today’s cells pack more than three times the energy density of those first-generation batteries. A typical pacemaker battery lasts 7 to 12 years depending on how often the device needs to pace your heart, after which a straightforward outpatient surgery swaps in a fresh generator.
The Lithium-Iodine Battery
Pacemakers use a lithium-iodine-polyvinylpyridine cell, a type of solid-state battery. The lithium anode reacts with an iodine-based cathode, and the chemical reaction between the two produces a small, steady electrical current. There’s no liquid electrolyte sloshing around. Instead, a thin solid layer of lithium iodide forms naturally at the boundary between the two materials and acts as both the electrolyte and a barrier, which makes the battery extremely stable and nearly impossible to leak.
This matters because a leaking battery inside your chest would be a serious problem. The solid-state design also means the battery’s voltage drops gradually and predictably as it depletes, giving doctors a reliable way to monitor how much life is left. The entire battery is typically about the size of a few stacked coins, and the titanium casing of the pacemaker hermetically seals it from body fluids.
How Long the Battery Lasts
Battery life varies quite a bit based on your individual pacing needs. A pacemaker that fires frequently to keep your heart rhythm steady draws more current than one that mostly monitors and only paces occasionally. Programming choices your cardiologist makes, like the voltage of each pacing pulse and the heart rate settings, also affect drain. Most traditional pacemakers last somewhere between 7 and 12 years, though some patients get longer.
Leadless pacemakers, which are tiny capsules implanted directly inside the heart, have smaller batteries by necessity. The Medtronic Micra AV2, for example, has a battery capacity of 142 milliamp-hours and a projected median longevity of about 10.9 years. The Abbott Aveir dual-chamber system uses two separate capsules: the one placed in the lower chamber holds 241 milliamp-hours with a median projected life of 9.9 years, while the smaller upper-chamber capsule holds 174 milliamp-hours and lasts roughly 5.3 years. That shorter lifespan in the upper capsule is a notable concern, especially for younger patients who may need multiple replacements over a lifetime.
How Doctors Know the Battery Is Dying
Your pacemaker doesn’t just stop working one day. It’s designed to give months of warning. During routine check-ups (often done remotely through a home monitor), your cardiologist can read the battery voltage. When the voltage drops to a specific threshold, typically around 2.5 volts for many devices, the pacemaker triggers what’s called an elective replacement indicator. At that point, the device automatically disables some non-essential features to conserve power and extend the remaining life.
A simpler bedside check involves placing a magnet over the pacemaker. In many models, a magnet rate below about 86 beats per minute signals that the battery has crossed into the replacement zone. Once the replacement indicator triggers, you generally have about three months before the battery reaches its true end of life. That’s enough time to schedule the replacement surgery without any emergency.
What Replacement Surgery Looks Like
Replacing a pacemaker battery means replacing the entire pulse generator, the sealed metal box that sits under the skin near your collarbone. The battery can’t be swapped out on its own because it’s permanently sealed inside. A surgeon opens the existing pocket in your chest, disconnects the old generator from the wire leads, removes it, and connects a new generator to those same leads. If the leads are still functioning normally, they stay in place. The whole process is an outpatient procedure similar to your original implant, and recovery is generally quicker since the pocket and leads already exist.
If you’re completely dependent on the pacemaker to maintain a heartbeat, your doctor will use a temporary pacing wire during the brief window when the old generator is disconnected and the new one isn’t yet hooked up. That temporary wire comes out as soon as the new device is working. In rare cases where a lead has malfunctioned, the leads themselves need replacement too, which is a more complex surgery.
Protection From Electromagnetic Interference
A sealed battery inside a titanium case is already well-shielded, but strong electromagnetic fields like those from an MRI machine can still pose problems. Starting in 2008, manufacturers began producing MRI-compatible pacemaker systems. These devices use less ferromagnetic material in their construction and include specific shielding around internal circuits to prevent the magnetic field from disrupting the power supply. They also have a dedicated MRI mode that your care team activates before a scan. The proportion of magnetic metals in modern devices and leads is low enough that the physical forces from an MRI won’t displace the hardware.
Before Lithium: The Plutonium Pacemaker
Between 1970 and 1977, a small number of pacemakers were powered by plutonium-238, using a radioisotope thermoelectric generator that converted the heat from radioactive decay into electricity. The appeal was obvious: the battery would outlast the patient. A plutonium-powered pacemaker implanted in 1973 was reported still working 34 years later. But the cost was high, the regulatory burden of implanting radioactive material was significant, and radiation safety concerns limited adoption. Once lithium-iodine batteries proved reliable and long-lasting enough, plutonium pacemakers became a historical curiosity. A handful of patients may still carry them today.
Experimental Power Sources
Researchers are exploring ways to power pacemakers without a battery at all, or at least without one that needs periodic replacement. The most promising approach harvests energy from the heart’s own motion. Piezoelectric materials generate a small voltage when they’re squeezed or bent, and the heart’s constant beating provides a reliable source of mechanical stress. In one proof-of-concept study, researchers measured the heart’s kinetic motion using a laser and designed a piezoelectric energy harvester small enough to fit inside a leadless pacemaker’s battery compartment. The device generated 1.1 volts from simulated cardiac motion, which is in the right ballpark for pacing needs.
Other approaches that work outside the body, like solar power or electromagnetic harvesting, don’t translate well to an implant deep in the chest. Biofuel cells that run on blood glucose produce too little power currently, and thermoelectric generators struggle because the temperature difference inside the body is too small to drive meaningful energy production. Piezoelectric harvesting paired with a tiny rechargeable battery remains the most plausible path, though none of these technologies have reached clinical use yet.