BV-5JW Nokia 800 Replacement Battery 3.7V 1450mAh Li-ion

Nokia Lumia 800 Series — 3.7V Li-ion Replacement Battery (BV-5JW)

This is a 3.7V Li-ion cell rated at 1450mAh (5.37Wh), built to the BV-5JW specification. It fits the Nokia 800, Lumia 800, Lumia 800C, and Sea Ray. It replaces the original cell when capacity fade makes the phone unreliable through a normal day.

• Lumia 800 family fit: The 800, Lumia 800, Lumia 800C, and Sea Ray share the same battery bay geometry, connector pinout, and BMS handshake protocol — one cell covers all four variants without modification.
• Bench tested on actual hardware: We ran the BV-5JW through full charge and load cycles on a Lumia 800. The BMS held charge termination at 4.2V and tripped low-voltage cutoff cleanly before cell voltage could drop below 3.0V under screen and modem load.
• First-cycle fuel gauge recalibration: After fitting this cell, disable fast charging and run one complete discharge-charge cycle before resuming normal use. The Lumia 800's fuel gauge IC was calibrated to the original cell's discharge curve — a full slow cycle lets it re-anchor to the new cell before high-current charging starts.

Why the Lumia 800 reports wrong battery percentage after a cell swap

The Lumia 800 uses a coulomb counter that builds its fuel map against the original cell's discharge curve over time. Swap the cell, and that map no longer matches what the new chemistry actually delivers. The OS reads a stale model, so it displays percentage that drifts away from real charge state. One full slow discharge to cutoff, then a full charge without interruption, forces the counter to relearn the new cell's curve.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff, not a capacity problem. Under combined modem and AMOLED screen load, the cell's terminal voltage sags faster than the fuel gauge expects — the phone hits the hardware undervoltage cutoff while the OS still shows charge remaining. It happens most often during calls or video playback. Complete two full discharge-charge cycles so the fuel gauge IC can map the new cell's voltage-versus-capacity curve accurately; the shutdowns typically stop by the third cycle.