About this replacement
Bang & Olufsen Beoplay H8i / H9 3rd Gen — 3.7V Li-Polymer Replacement Battery (AEC723938)
This 3.7V, 1000mAh Li-Polymer cell replaces the internal battery in the Beoplay H8i and Beoplay H9 3rd Generation wireless over-ear headphones. It restores power capacity to both wireless audio playback and active noise cancellation. At 39.50 x 38.00 x 6.00mm, it matches the original cell footprint exactly.
- H8i and H9 3rd Gen shared platform: Both headphones run the same 3.7V cell with the same connector and BMS handshake. The AEC723938 part number covers both models — the fuel gauge calibration and charge termination logic carry over between them without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the H8i platform. The BMS accepted the cell cleanly, charge termination fired at the correct cutoff voltage, and ANC draw did not trigger any protection events.
- Fuel gauge reset after swap: After fitting this cell, let the headphones discharge fully until they power off, then charge uninterrupted to 100% before use. Skipping this step leaves the fuel gauge reading from the old cell's history, which causes the battery indicator to report inaccurate levels from the first use.
Why the H8i shows a full charge bar but cuts out during ANC use
ANC draws a separate continuous current on top of the audio amplifier load. When the cell has aged, its internal resistance rises enough that combined ANC-plus-amp draw causes a voltage sag the BMS reads as a low-cell event — even if the reported state of charge looks healthy. The headphones shut down to protect the cell. A new cell at lower internal resistance eliminates the sag that triggers that cutoff. After fitting the replacement, run the full discharge-recharge calibration cycle so the fuel gauge tracks the new cell accurately.
Battery indicator stuck at one bar well before audio actually stops
This happens when shallow charging — topping off at 60–80% repeatedly without ever completing a full cycle — causes the fuel gauge to lose track of the cell's true capacity endpoints. The indicator hits its lowest threshold early because the calibration floor is set too high. It is not a fault with the new cell. Discharge fully until the headphones power off automatically, then charge to 100% in one uninterrupted session; that resets the calibration endpoints and the indicator will track correctly down to the real 3.0V cutoff floor.