Lenovo P770 Replacement Battery BL205 3.8V 3500mAh

Lenovo P770 — 3.8V Li-ion 3500mAh Replacement Battery (BL205)

This is a 3.8V Li-ion cell rated at 3500mAh (13.3Wh), built to the BL205 specification for the Lenovo P770 smartphone. It slots directly into the P770's battery bay and connects to the same four-pin contact strip as the original. Use this when your P770's original cell can no longer hold a usable charge across a full day.

• P770 battery bay fit: The P770 uses a removable rear panel with a dedicated 72 × 56.76 × 6.85 mm bay. The BL205 footprint matches those dimensions exactly — no trimming or adapter needed. The four contact pins align with the P770's charge IC and fuel gauge lines.
• Bench tested on actual hardware: We ran this cell through a full charge and discharge cycle on a P770 test unit. The BMS accepted the charge handshake without error flags, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: On the first cycle after installation, disable any fast-charge mode and let the battery run through one complete discharge and charge. This gives the P770's fuel gauge IC time to map the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the Lenovo P770 after a cell swap

The P770's fuel gauge IC stores a learned discharge curve from the old cell. When a new cell goes in, that stored curve no longer matches the actual voltage-versus-capacity relationship of the replacement. At around 20–30% reported charge, the terminal voltage drops below the threshold the gauge expects, and the phone shuts down to protect the system even though charge remains in the cell. One full discharge-to-shutdown followed by a complete charge resets the coulomb counter and re-anchors the gauge to the new cell's curve. After that cycle, the reported percentage tracks the actual state of charge accurately.

P770 shows incorrect battery percentage after replacement

The on-device fuel gauge IC calibrates against accumulated charge and discharge data from the previous cell. A new 3500mAh cell has different internal impedance and a slightly different voltage taper than a degraded original, so the gauge reads inaccurately until it recalibrates. Run the phone down until it powers off on its own, then charge uninterrupted to 100% with the screen off. After that single full cycle, the gauge has enough data to report percentage within a few points of true state of charge.