About this replacement
Bookeen Cybook Muse HD — 3.7V Li-Polymer Replacement Battery (JL315889PL)
This 3.7V, 2000mAh Li-Polymer cell replaces the original JL315889PL battery in the Bookeen Cybook CYBFT1F-BK and Cybook Muse HD e-readers. Both devices share the same battery footprint, connector, and BMS communication protocol. Capacity figure is taken directly from product specification — 7.4Wh total energy.
- CYBFT1F-BK and Muse HD compatibility: Both models run the same internal power rail at 3.7V nominal and use an identical flat Li-Polymer cell with the same physical dimensions and connector pinout. One cell fits both without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a Muse HD unit. The BMS accepted the new cell without fault flags, and the firmware completed its recalibration pass within one full charge cycle.
- Post-swap charge cycle on Muse HD: After installing this cell, connect via USB and charge completely before reading. The Cybook firmware recalibrates its battery percentage display against a full-charge reference point — skipping this step causes the indicator to read inaccurately for several sessions.
Why the Cybook Muse HD shows low battery immediately after a new cell
Replacement cells ship at storage voltage — typically 3.6V to 3.85V — which sits below the firmware's calibrated full-charge threshold of around 4.2V. The Muse HD reads this as a partially depleted battery, not a fresh one. This is a firmware calibration issue, not a cell defect. Connect to USB power and charge fully before the first use to reset the reference point.
Battery percentage jumping erratically after swap on CYBFT1F-BK
The CYBFT1F-BK tracks charge state using a coulomb counter that calibrates itself against the installed cell's actual capacity over the first few cycles. A new cell resets this learned profile, causing the displayed percentage to jump during early use. This settles after two or three complete charge-discharge cycles. If jumps persist beyond three cycles, verify the cell voltage reads at least 4.1V at the top of a full charge.