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Lithium-ion batteries are the heart of modern devices—smartphones, laptops, electric vehicles, and more. Their high energy density powers our daily lives, but they also come with potential risks of fire or explosion if not properly managed. Behind the scenes, the Battery Management System (BMS) ensures safety, longevity, and optimal performance. This article explores the key functions of BMS, how it works, and why it is essential for lithium-ion battery safety, with real-world examples of what happens when BMS is absent or fails.     What is a BMS? A Battery Management System (BMS) is an electronic control system that monitors and manages the condition of lithium-ion battery packs. It does more than just measure voltage and current; it safeguards the battery by controlling charging and discharging processes, balancing cells, and providing data on battery health. In electric vehicles, drones, and large energy storage systems, a BMS is not optional—it’s critica...

When diagnosing battery packs, especially BMS boards that are not outputting voltage, checking the gate voltage of MOSFETs is a fundamental diagnostic step. This test can distinguish between a FET issue and a control IC issue.     1. Why Gate Voltage Matters MOSFETs act as electronic switches. Unless a sufficient gate-source voltage (Vgs) is applied, the MOSFET remains off and no current flows between drain and source. Gate: Controlled by the BMS's protection IC Source: Usually tied to B− (battery negative) Drain: Connected to P− (load or charge return path)     2. Step-by-Step Gate Voltage Test Set your multimeter to DC voltage mode. Connect the black probe to B− (usually battery negative terminal). Touch the red probe to the gate leg of the MOSFET (usually the leftmost or rightmost pin). Check the voltage. Typically, a Vgs above 2–4V indicates the MOSFET is in conduction (on) state. If gate voltage ...