Sony WH-H800 Charging Case Compatible Battery 3.7V 300mAh

Sony WH-H800 Charging Case — 3.7V Li-Polymer Replacement Battery (ACE621733)

This 3.7V 300mAh Li-Polymer cell replaces the internal battery inside the Sony WH-H800 charging case. It fits the portable case unit — not the headphones themselves. Without a functional case battery, the case cannot store charge or top up the headphones between uses.

• WH-H800, WF-XB700, and WF-C500 case compatibility: These Sony charging cases share a compact Li-Polymer cell on the same 3.7V rail with the same footprint and connector orientation. All three use the ACE621733 cell to power the internal charge management circuit that feeds the headphone pods.
• Bench tested on actual hardware: We cycled this cell through the case's charge controller and confirmed the BMS accepted the new pack without a charge fault. Current draw through the case output matched the original cell's behaviour under load.
• Case recalibration after swap: After fitting the new cell, run the case battery fully down until the LED indicator goes out, then charge it uninterrupted to 100%. The case controller re-maps the cell capacity on that first full cycle — skipping it causes the LED status to misread remaining charge.

Why the charging case LED shows full but the headphones cut off after short use

A degraded case battery often sits at a surface voltage that reads as full to the LED circuit but collapses under the load of actively charging the headphone pods. The case controller reads open-circuit voltage — not actual capacity. Once current flows into the headphones, the cell sags below the controller's cutoff threshold and the output shuts down. Replacing the cell and completing one full discharge-charge cycle gives the controller an accurate capacity baseline.

Case not charging the headphones after a new cell is fitted

If the headphones sit in the case but show no charge transfer, the case controller may not have completed its BMS handshake with the new cell. This happens when the replacement cell arrives at storage voltage — roughly 3.6V — and the controller holds the output circuit open until it confirms the cell is above its activation threshold. Place the case on charge via USB first, wait for the LED to confirm the case itself is charging, then seat the headphones. Once the case cell clears 3.7V, the output circuit releases and charging resumes normally.