Battery Diagnostics Move onto the Monitor Chip

Texas Instruments has put an electrochemical impedance spectroscopy engine directly on a battery monitor die. The BQ79826Z-Q1 monitors 26 cells — eight more channels than any competing monitor, according to TI — and is designed for 104-cell module architectures, so four devices cover a full module while minimising bill of materials and cost per channel.

EIS is the technique that separates a battery management system that measures from one that diagnoses. Voltage and current tell you the state of charge and, with enough history and modelling, a rough estimate of health. Impedance spectroscopy applies a small excitation across a range of frequencies and measures the cell's response, which resolves the internal processes that voltage alone cannot distinguish — charge transfer, diffusion, film growth on the electrodes. That is what makes it possible to separate a temporarily depressed state of charge from permanent chemical degradation such as lithium plating.

Lithium plating is the specific failure worth caring about. It occurs when charging is too fast or too cold for the anode to absorb lithium into its structure, so metallic lithium deposits on the surface instead. It permanently removes capacity, and the dendrites it forms are the mechanism behind internal short circuits — which is to say, it is both a degradation problem and a safety problem, and it is invisible to a voltage-only monitor until it has progressed a long way.

Integrating EIS onto the monitor is what makes it deployable at grid scale. The technique has existed for decades in laboratories, where it needs a potentiostat and a bench. Removing that add-on hardware also produces cleaner impedance curves, and TI says the raw chemical-level data is exposed so developers can run their own proprietary algorithms on it rather than a fixed vendor health estimate — which matters, because state-of-health estimation is where storage operators differentiate.

Henrik Mannesson, TI's general manager for grid infrastructure and power delivery, is quoted on the separation of charge state from chemical degradation. The part is currently sampling as pre-production silicon, with full volume production expected by the end of 2026 and first commercial systems shipping as early as 2027 — so this is a design-in decision now rather than a procurement one.