Lenovo BL243 K3 Note Replacement Battery 3.7V 2000mAh

Lenovo K3 Note / K50-T5 — 3.7V Li-ion Replacement Battery (BL243)

This is a 3.7V, 2000mAh (7.4Wh) Li-ion replacement battery for the Lenovo K3 Note smartphone. It carries OEM part number BL243 and fits the K3 Note, K50-T5, Lemon K3 Note, and K50-T3s. If your phone shuts down unexpectedly, holds a charge poorly, or won't power on, a worn cell is the likely cause.

• K3 Note / K50-T3s / K50-T5 platform fit: All four listed models share the same physical footprint, connector pinout, and BMS handshake requirements under the BL243 spec. Swapping between any of these variants does not require a firmware change or connector adapter.
• Bench tested on actual hardware: We cycled this cell on a K3 Note board and confirmed the BMS accepted the charge profile without triggering a fault cutoff. The protection circuit responded correctly to both charge termination and low-voltage disconnect events.
• First-cycle fuel gauge calibration: After installation, disable fast charging and run one full discharge-to-charge cycle before enabling high-current charging. The fuel gauge IC is calibrated to the old cell's discharge curve — one slow cycle lets it remap against the new cell before fast charge pushes current into an uncalibrated state.

Why the K3 Note reports wrong battery percentage after a cell swap

The K3 Note uses a coulomb counter that builds its percentage model from accumulated charge and discharge data on the original cell. When you install a new cell, that learned curve no longer matches the new cell's actual discharge characteristics. The OS reads from a stale internal map, so the reported percentage can appear frozen, inflated, or out of step with real remaining capacity. One full discharge from 100% to automatic shutdown, followed by an uninterrupted charge to 100%, forces the coulomb counter to rebuild its reference curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff, not a calibration error. Under high-draw moments — screen at full brightness, mobile data active, or a background sync burst — the cell voltage drops sharply and briefly falls below the BMS low-voltage cutoff threshold, triggering an immediate shutdown even though the gauge still shows charge remaining. A degraded or deeply discharged new cell has higher internal impedance, which makes the voltage sag worse under load. Charge the replacement fully before first use, and if shutdowns persist after one calibration cycle, check that the battery connector is fully seated with no bent pins.