About this replacement
Kobo Aura HD (N204-KBO-B) — 3.7V Li-Polymer Replacement Battery (SP305590)
This is a 3.7V, 1500mAh Li-Polymer replacement battery for the Kobo Aura HD e-reader (model N204-KBO-B). It matches the OEM part number SP305590 and fits the thin 84.50 × 49.00 × 2.80mm cell cavity inside the Aura HD chassis. Install this when the original cell no longer holds enough charge to get through a reading session.
- Aura HD and N204-KBO-B fitment: Both the Aura HD retail and N204-KBO-B variants use the same connector pinout, cell dimensions, and BMS communication protocol — so one cell covers both board revisions without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Aura HD board. The BMS accepted the cell without faults, charge termination triggered correctly at full voltage, and the firmware reported state-of-charge without errors.
- Post-swap charge cycle on the Aura HD: After fitting the new cell, connect via USB and let it charge completely before powering on. The Aura HD firmware reads cell voltage to calibrate its battery percentage display — skipping this step causes the indicator to jump or misreport from the first boot.
Why the Aura HD shows incorrect battery percentage after a cell swap
The Aura HD firmware tracks battery state by mapping voltage curves from the original factory cell. A new cell starts at storage voltage — typically around 3.7V — which sits mid-range on the old curve, so the firmware reports a false percentage. A full charge-discharge cycle lets the firmware re-anchor its voltage-to-percentage mapping to the new cell's actual curve. Until that recalibration completes, the percentage display will drift or jump between readings.
Aura HD not powering on after battery replacement
If the Aura HD shows no response after fitting the new cell, the cell voltage has likely dropped below the device's minimum boot threshold during storage — typically under 3.0V. Connect the device to a USB charger and leave it for 10 minutes before attempting to power on; this gives the BMS enough headroom to initialise the charging circuit. After that pre-charge window, the device should respond to the power button. If the screen remains blank, confirm the battery connector is fully seated — the Aura HD connector can appear locked while still sitting slightly off the board contacts.