Defibrillator batteries are used in both internal and external defibrillators. In an internal defibrillator, or defibrillator implant, the entire defibrillator is placed in the person’s chest. The battery in a defibrillator implant sends a charge through an electrode wire. The electrode wire is actually placed in a vein in the heart’s chamber. This allows it to deliver the shock immediately when it detects and irregular heartbeat. Defibrillator implants are only placed in people who have serious heart conditions.