About this replacement
Sony Ericsson A2638 Series — 3.7V Li-ion Replacement Battery (BHC-11)
This is a 3.7V 1400mAh Li-ion replacement for the original BHC-11 battery. It fits the Sony Ericsson A2638, A2218, A2618s, and R300 — phones that share the same battery bay dimensions and connector pinout. Capacity matches the factory cell at 1400mAh (5.18Wh).
- A2638 / A2218 / R300 platform fit: These models use the same 3.7V rail, identical connector orientation, and a shared BMS handshake protocol. One battery revision covers the full range without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the A2638 platform. The BMS accepted charge current without fault flags, and voltage held stable under modem-active load across the full discharge curve.
- Fuel gauge recalibration on first use: After installing this cell, run one full uninterrupted discharge down to automatic shutdown, then charge to 100% without interruption. This gives the fuel gauge IC a clean reference curve for the new cell before the OS starts reporting percentage to the user.
Why the A2638 reports wrong battery percentage after a cell swap
The A2638 uses a coulomb-counting fuel gauge IC that builds its charge model against the original cell's discharge curve. When a new cell goes in, the IC still references the old curve — so the percentage shown on screen doesn't match actual cell state. The mismatch can show up as a sudden jump from 40% to full, or a slow drain that reads 60% right until shutdown. One complete discharge-charge cycle resets the counter and trains the IC against the new cell's actual curve.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff issue, not a capacity fault. Under peak load — active call, screen at full brightness, radio scanning — cell voltage can drop faster than the fuel gauge IC expects, hitting the BMS low-voltage cutoff while the display still shows 20–30%. The BMS trips at approximately 3.0V per cell to protect the chemistry. After shutdown, leave the phone off and place it on charge immediately; this lets the cell recover above the cutoff threshold before you power on again.