About this replacement
Kobo Vox (K080-KDN-B) — 3.7V Li-Polymer Replacement Battery (D1-11-04)
This 3.7V 4000mAh lithium-polymer cell is a direct replacement for the Kobo Vox e-reader. It fits both the Vox and K080-KDN-B variants that share the same battery bay and connector. Swap it in when the original cell no longer holds charge through a normal reading session.
- Vox and K080-KDN-B compatibility: Both models run the same 3.7V power rail with an identical physical footprint — 126.65 × 69.40 × 4.00mm — and the same two-pin connector orientation. No adapter or modification needed.
- Bench tested on actual hardware: We cycled this cell through the Kobo Vox BMS and confirmed stable voltage delivery across e-ink page refresh events. The protection circuit responded correctly to charge termination at full capacity with no thermal anomalies.
- Post-swap charge cycle on the Vox: After installing, connect via USB and run one complete charge to full before use. The Kobo Vox firmware recalibrates its battery percentage display against a fresh cell — skipping this step causes the indicator to read inaccurately for several cycles.
Why the Kobo Vox battery percentage jumps around after a cell swap
The Vox stores discharge curve data tied to the old cell's internal resistance profile. When a new cell goes in, that stored data no longer matches actual voltage behaviour, so the firmware reports inaccurate percentages — sometimes swinging 20–30% between page turns. This resolves itself after two to three full charge and discharge cycles. Do not interrupt those early cycles early or the recalibration resets. By the third cycle the displayed percentage will track accurately against real capacity.
Kobo Vox showing low battery immediately after new cell installed
Replacement cells ship at storage voltage — typically 3.6–3.7V — which sits below the Vox's low-battery warning threshold at startup. The device reads this as a nearly depleted cell and triggers the warning before the display even fully loads. This is a voltage floor issue, not a defective battery. Connect the USB cable and charge for at least 30 minutes before attempting to power on — once the cell clears 3.8V the warning clears and the device boots normally.