About this replacement
Logitech UE9000 — 3.7V Li-Polymer Replacement Battery (75.211561)
This 3.7V, 450mAh Li-Polymer cell replaces part number 75.211561 in the Logitech UE9000 over-ear Bluetooth headphones. It restores wireless audio playback, active noise cancellation, and call functionality when the original cell has degraded. Dimensions are 31.10 × 30.00 × 5.00mm — confirm these against your existing cell before fitting.
- UE9000 fitment: The UE9000 uses a slim Li-Polymer pouch cell to fit within the ear cup housing. The 3.7V nominal rail matches the headset's audio amplifier and Bluetooth radio voltage requirements. Any deviation in cell thickness or footprint will prevent the ear cup from closing correctly.
- Bench tested on actual hardware: We cycled this cell through the UE9000's charging circuit and confirmed the BMS accepted charge termination correctly. Current draw under simultaneous Bluetooth streaming and noise-cancellation load stayed within the cell's rated discharge window.
- First-cycle behaviour on the UE9000: After fitting, place the headset on charge for a complete cycle before use. The UE9000's firmware uses the first full charge cycle to calibrate its talk-time estimate — skipping this step causes the indicator to read inaccurately for several sessions.
Why the UE9000 cuts out mid-call on a new battery
The UE9000 draws current from two loads simultaneously during a call — the Bluetooth radio and the active noise-cancellation circuit. A new cell at partial or storage charge has a higher internal resistance than a fully conditioned cell. Under combined load, the voltage sags briefly below the BMS cutoff threshold, triggering a shutdown. Running two or three full charge cycles brings internal resistance down and eliminates the dropout.
Talk time shorter than rated across the first few uses
Li-Polymer cells do not reach full capacity on the first cycle out of storage. The UE9000's rated talk time assumes a conditioned cell, not a fresh replacement. Capacity builds incrementally over three to five full charge and discharge cycles. After that break-in period, talk time should align with Logitech's published figures for the UE9000.