# Squeeze More Energy from Dead Batteries Using Physics Revive your batteries with a joule thief circuit. - **Source:** [Science Latest](https://brifing.si/source/ebc20f22-8d1a-4ae4-ba4c-efcd0853ba19) - **Published:** 2026-08-18 - **Topic:** [Software & Engineering](https://brifing.si/c/engineering) - **Original article:** - **On Brifing:** https://brifing.si/s/c5acabe3-3523-4f1d-8cb2-d51fef1a6384 ## Are Dead Batteries Really Dead? Even when batteries seem completely drained, they still contain chemical energy. The voltage doesn’t drop to zero but becomes insufficient to power devices. A physical circuit, like the joule thief, can tap into this residual energy, allowing devices to run longer. ## How Does the Joule Thief Circuit Work? The joule thief circuit uses a transformer and transistor to boost low voltage. The transformer creates a higher voltage in the secondary circuit through magnetic field changes. The transistor rapidly switches the current, enabling this process. This allows even a single battery to power an LED. ## Faraday’s Law and Applications Faraday’s law of induction explains how changing magnetic fields generate voltage. This principle is used in devices from electric generators to induction stoves. The joule thief circuit relies on this law to extract maximum energy from low-voltage batteries. ## The Role of the Transistor The transistor acts like a valve for electricity. In the joule thief circuit, it switches the current thousands of times per second. This rapid change induces a higher voltage in the transformer. Without the transistor, this process wouldn’t be possible. ## Building the Circuit The joule thief circuit consists of a battery, transformer, transistor, and LED. The primary circuit connects to the battery, while the secondary circuit connects to the LED. The transistor controls the current, making the circuit functional. This simple setup can be easily built at home. ## Advantages of LEDs Using LEDs instead of incandescent bulbs increases energy efficiency. LEDs emit light without generating heat, consuming less energy. However, LEDs require higher voltage, which the joule thief circuit provides. ## The Power of Magnetic Fields The strength of the magnetic field in the transformer is crucial for boosting voltage. Materials like iron rings enhance the magnetic field, increasing the transformer’s effectiveness. The number of turns in the secondary coil also plays a key role. ## Energy Savings and the Environment The joule thief circuit extends battery life, promoting energy savings. This is both economically and environmentally beneficial. It reduces battery waste, contributing to nature, while enabling small household devices to operate longer. ## Sources covering this story - https://www.wired.com/story/squeeze-more-juice-out-of-a-dead-battery/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._