BL223 Lenovo K920 Replacement Battery 3.8V 4000mAh

Lenovo K920 / VIBE Z2 Pro — 3.8V Li-Polymer Replacement Battery (BL223)

This is a 3.8V, 4000mAh Li-Polymer replacement battery for the Lenovo K920, K7, and VIBE Z2 Pro smartphones. OEM part number BL223. It fits directly into the existing battery bay and connects to the stock charge management circuit.

• K920 and VIBE Z2 Pro compatibility: The K920 and VIBE Z2 Pro share the BL223 footprint, connector pinout, and 3.8V nominal voltage rail. The BMS handshake on these models does not require a coded cell — the charge IC authenticates via voltage profile and thermistor, not a serial negotiation.
• Bench tested on actual hardware: We ran this cell on a K920 test unit and confirmed the BMS accepted charge from both USB and the onboard fast-charge path. The protection circuit tripped correctly at low-voltage cutoff during a full discharge cycle with no false shutdowns above 3.2V.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the K920 after a cell swap

The K920's fuel gauge IC stores a discharge curve learned from the original cell. A new cell has a different internal resistance profile, so the IC underestimates remaining capacity and hits a voltage cliff earlier than the percentage shown on screen. Under modem or display load, the cell voltage sags below the BMS cutoff threshold — usually around 3.2V — before the OS gauge reaches zero. One full slow discharge-charge cycle resets the learned curve and stops these early shutdowns.

Device not powering on after the replacement cell sat in storage

Li-Polymer cells self-discharge during storage. If the BL223 cell drops below approximately 2.5V, the BMS enters lockout mode to prevent cell damage and will refuse to pass current to the device. The phone will show no response — no charge indicator, no boot attempt. Connect to a wall charger rather than a USB port and leave it for 20–30 minutes; the charger's higher current floor is more likely to wake the BMS than a low-output USB port. Once the cell recovers to around 3.0V, the phone will boot normally.