About this replacement
Lenovo K9 Note — 3.8V Li-Polymer Replacement Battery (BL287)
This is a 3400mAh Li-Polymer replacement battery for the Lenovo K9 Note smartphone. It runs at 3.8V nominal (12.92Wh) and carries OEM part number BL287. It replaces the original cell when capacity has dropped or the phone no longer holds charge through a normal day.
- K9 Note cell fit: The BL287 footprint measures 80.00 × 63.20 × 4.10mm — the K9 Note chassis is sized around this exact cell. The connector and BMS handshake are matched to the phone's charge IC, so the system recognises the new cell without triggering a fault state.
- Bench tested on actual hardware: We cycled BL287 cells through the K9 Note charge IC and confirmed the BMS communication line exchanges correctly with Lenovo's fuel gauge IC. Charge current ramp and cutoff voltage behaved as expected at 4.35V full charge.
- First-cycle fuel gauge calibration: On first use after fitting, disable fast charging and run one complete discharge-to-charge cycle. The fuel gauge IC calibrates its coulomb counter against the new cell's discharge curve before high-current charging is introduced into an uncalibrated system.
Sudden shutdown at 20–30% on the K9 Note after a cell swap
This happens because the fuel gauge IC is still running the discharge curve from the old, degraded cell. When the new BL287 cell reaches a voltage point the IC incorrectly maps to 20–30%, the modem or display pulls a current spike that drops cell voltage below the BMS protection threshold instantly. The phone shuts down even though usable capacity remains. One full discharge-charge cycle — without fast charging — resets the coulomb counter and maps the new cell's voltage curve correctly.
USB fast charge not engaging on the first charge after replacement
The K9 Note's charge IC runs a handshake with the BMS on the new cell before it authorises elevated charge current. On the very first cycle, the IC defaults to standard 5V input until it confirms cell impedance is within range. This is normal behaviour — fast charging typically re-engages from the second cycle onward once the BMS has completed its initialisation sequence. If fast charging still does not engage after two full cycles, check the USB cable is rated for the phone's charging protocol.