About this replacement
Lenovo A66T — 3.7V Li-ion Replacement Battery (BL181)
This is a 3.7V, 1750mAh Li-ion replacement battery for the Lenovo A66T smartphone. It replaces OEM part BL181 directly and fits the standard battery bay on the A66T. Voltage and capacity match the original cell specification exactly.
- A66T battery bay fit: The A66T uses a removable rear-cover design with a dedicated battery bay. BL181 cells share the same contact pin layout and physical dimensions (64.78 × 43.78 × 4.89mm), so the connector seats without forcing.
- Bench tested on actual hardware: We cycled this cell through a full discharge and charge sequence on the A66T. The onboard charge IC accepted the cell without fault flags, and the BMS held voltage within the expected window across the full charge curve.
- Fuel gauge recalibration on first use: On first install, disable fast charging if your network supports it, then run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before any high-current session runs into an uncalibrated baseline.
Why the A66T reports wrong battery percentage after a cell swap
The A66T uses a fuel gauge IC that builds its capacity model from accumulated charge and discharge cycles on the original cell. When you install a new cell, the IC still references the old degraded curve. This causes the percentage readout to drift — often reading higher than actual early in discharge, then dropping sharply. One full discharge from 100% to automatic shutdown, followed by a complete uninterrupted charge, resets the coulomb counter reference. After that single cycle, percentage accuracy normalises.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem, display backlight, or GPS pulls a short current spike and the cell voltage drops below the BMS cutoff threshold — even though the gauge still reads 20–30%. A fresh cell at 1750mAh has more headroom than a worn original, but an uncalibrated fuel gauge doesn't know that yet. The phone interprets the momentary voltage sag as a critical low and cuts power to protect the cell. Run the recalibration cycle described above first; if shutdown persists after that, check that the battery contacts on the phone are clean and seating flat — a high-resistance connection amplifies voltage sag under load.