About this replacement
Lenovo A900 — 3.7V Li-ion Replacement Battery (BL123)
This is a 3.7V, 900mAh Li-ion cell built to replace the original BL123 battery in the Lenovo A900 smartphone. It fits the A900 directly, restoring power to a phone that no longer holds charge or fails to turn on. Capacity matches the stock specification at 3.33Wh.
- Lenovo A900 fitment: The A900 uses the BL123 cell on a 3.7V rail with a specific connector pitch and BMS handshake tied to the phone's charge IC. This replacement matches that connector and communicates correctly with the A900's charging circuit — no adapter or modification needed.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the A900 platform and confirmed the BMS negotiated correctly with the charge IC. Cutoff voltage held at the expected floor and the cell accepted a full charge without triggering a protection fault.
- Fuel gauge recalibration on first install: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its discharge curve against the new cell before high-current charging pushes current into an uncalibrated state.
Sudden shutdown at 20–30% on the Lenovo A900 after a cell swap
The A900's fuel gauge IC was calibrated to the discharge curve of the original, degraded cell. When a fresh cell with a different internal resistance profile is installed, the gauge misreads the remaining capacity. Under load — modem radio, screen at full brightness — the actual cell voltage drops faster than the gauge predicts, hitting the cutoff threshold while the display still shows 20–30%. One full discharge-charge cycle lets the coulomb counter reset its model against the new cell's actual curve, and the shutdowns stop.
A900 not powering on after the battery sat in storage
Li-ion cells that have been stored discharged for weeks can drop below 2.5V per cell, triggering a BMS lockout that blocks normal charging. The phone will show no response on the charger and won't boot. Connect the phone to a wall charger — not a computer USB port — and leave it for 20–30 minutes without pressing any buttons. The charge IC on most A900 units will trickle current into the cell at a low rate until voltage climbs above the BMS recovery threshold, typically around 2.9V, at which point normal charging resumes.