BV-5J Microsoft Lumia 435 Replacement Battery 3.7V 1550mAh

Microsoft Lumia 435 / 532 — 3.7V Li-ion Replacement Battery (BV-5J)

This is a 3.7V 1550mAh Li-ion cell built to the BV-5J specification, fitting the Microsoft Lumia 435, Lumia 532, and RM-1070. It replaces the original cell when the phone can no longer hold charge through a standard day or shuts down unexpectedly under load. Dimensions are 60.10 × 38.10 × 5.60 mm — measure your existing cell before ordering if you are unsure.

• Lumia 435, 532, and RM-1070 compatibility: All three models run the same voltage rail and use an identical connector footprint with the same BMS handshake protocol, which is why Microsoft used one part number — BV-5J — across the entire range.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Lumia 435 unit and confirmed the BMS communicated correctly with the charge IC, with no false cutoffs or thermal flags during a full charge cycle.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. This lets the Lumia's coulomb counter map its readings to the new cell's actual discharge curve.

Why the Lumia 435 reports wrong battery percentage after a cell swap

The Lumia 435 uses a fuel gauge IC that tracks charge by counting coulombs against a stored discharge curve from the original cell. A new cell has a slightly different internal resistance profile, so the stored curve no longer matches what the hardware is measuring. The gauge starts reporting percentages that are off — sometimes by 15–20 points. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to rewrite its reference curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the combined load of the modem radio and display — a voltage cliff the fuel gauge did not predict because it was still running the old cell's curve. The phone's protection circuit reads the voltage drop as a hard undervoltage event and cuts power before the gauge reaches 0%. After one full recalibration cycle, the gauge learns where the new cell's voltage cliff sits and the early shutdowns stop. If they persist past two full cycles, check that the cell is seated flat with no gap at the connector — a loose contact raises effective impedance and worsens the sag.