About this replacement
Plantronics Backbeat Fit 3100 Wireless Charging Case — 3.7V Li-Polymer Replacement Battery (AHB762240)
This 3.7V, 600mAh Li-Polymer cell replaces part number AHB762240 inside the Plantronics Backbeat Fit 3100 and Backbeat Fit 3200 Wireless Charging Cases. The case battery powers the dock itself — when it fails, the case can no longer wirelessly charge the earbuds without being tethered. Swapping this cell restores cordless charging functionality to the case.
- Backbeat Fit 3100 and 3200 case compatibility: Both cases share the same AHB762240 cell, voltage rail, and physical footprint. The BMS in each case communicates with the same charge management IC, so one replacement covers both enclosures without modification.
- Bench tested on actual hardware: We cycled this cell through the case's wireless charging circuit and confirmed the BMS accepted the new pack without flagging a protection trip. Charge acceptance and cutoff voltage both matched factory spec at 4.2V.
- First-cycle case conditioning: After fitting the new cell, run the case through one complete charge via its USB-C port before placing the earbuds inside. The case firmware recalibrates its internal fuel gauge on that first full cycle — skipping it can cause the LED indicator to misread remaining capacity.
Why the Backbeat Fit 3100 case LED shows full but earbuds cut off quickly
When the original cell degrades, its internal resistance rises sharply. The case voltage under load drops faster than the BMS expects, so the LED reads a higher state of charge than the cell can actually deliver. The earbuds draw current from the case during wireless charging — even a brief combined load collapses the sagging cell's output. Running the replacement through two or three full charge-discharge cycles resets the fuel gauge and brings the LED reading back into line with real capacity.
Case not charging earbuds after battery replacement — no LED activity
A freshly installed cell often sits at storage voltage, typically around 3.6V, which can cause the case's protection circuit to withhold output to the Qi coil until the cell is topped up. Connect the case to USB-C power for at least 30 minutes before placing the earbuds in the dock. If the LED still does not respond, hold the case button for 10 seconds to force a BMS re-initialisation. The charging coil should activate once the cell clears 3.7V.