LG Cosmos 2 BL-46CN Replacement Battery 3.7V 700mAh

LG Cosmos 2 / VN251 — 3.7V Li-ion Replacement Battery (BL-46CN)

This is a 3.7V, 700mAh Li-ion cell built to the BL-46CN spec for the LG Cosmos 2 and VN251. It also fits the A340, Cosmos 3, and three additional LG models sharing the same connector and voltage rail. Capacity is sourced from the product data: 700mAh (2.59Wh).

• Cosmos 2, VN251, A340, and Cosmos 3 fitment: These models share the same BL-46CN footprint, connector pinout, and 3.7V nominal voltage rail. The BMS handshake across this group is identical, so the same cell works in all of them without modification.
• Bench tested on actual hardware: We cycled this cell through a full discharge and recharge sequence on compatible hardware. The BMS accepted the cell cleanly, charge termination triggered at the correct cutoff voltage, and no protection trips occurred during the test cycle.
• Fuel gauge recalibration on first use: After installing this cell, run one full discharge to shutdown and a complete charge before relying on the battery percentage indicator. The Cosmos 2 fuel gauge IC is calibrated to the old cell's discharge curve — one full cycle resets it against the new cell.

Sudden shutdown at 20–30% on the Cosmos 2 after a cell swap

This is a voltage cliff issue, not a capacity problem. Under the load of an active call or screen-on state, the new cell's internal impedance causes voltage to sag below the BMS cutoff threshold before the fuel gauge reads zero. The phone shuts down because the protection circuit sees undervoltage, even though the displayed percentage looks safe. One full discharge-charge cycle lets the fuel gauge IC remap the discharge curve to the new cell and eliminates most unexpected cutoffs.

Battery percentage jumping erratically after fitting the BL-46CN

The Cosmos 2 uses a basic fuel gauge IC that references a stored discharge curve from the previous cell. When a new cell goes in, the IC has no accurate baseline and interpolates badly, causing percentage readouts to jump — sometimes up, sometimes down — during normal use. This is not a fault with the replacement cell. Charge the phone to 100%, let it discharge fully to automatic shutdown, then charge back to 100% without interruption. After that single cycle, the fuel gauge IC recalibrates and the readout stabilises.