Microsoft Lumia 550 Compatible Battery BL-T5A 3.8V 2200mAh

Microsoft Lumia 550 / Lumia 730 / Lumia 735 — 3.8V Li-ion Replacement Battery (BL-T5A / BV-T5A)

This is a 3.8V, 2200mAh Li-ion battery replacing OEM part numbers BL-T5A and BV-T5A. It fits the Microsoft Lumia 550 (RM-1127), Lumia 730, and Lumia 735, along with six additional Lumia variants sharing the same cell form factor. If the original battery no longer holds a charge through a normal day of calls, messaging, and apps, this cell restores that capacity.

• Lumia 550 / 730 / 735 platform fit: These models share the BL-T5A/BV-T5A cell specification — same 3.8V nominal rail, same 82.30 x 40.00 x 5.20mm footprint, and the same connector pinout. The BMS handshake on these Lumia devices authenticates by cell voltage curve, not a cryptographic ID, so a correctly specced replacement cell is accepted by the charge IC without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Lumia 550 unit. The BMS accepted the cell immediately, charge current ramped normally through CC/CV phases, and the protection circuit tripped correctly at the low-voltage cutoff — no anomalies at any point in the cycle.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-to-charge cycle before normal use. The Lumia fuel gauge IC holds calibration data from the old cell's discharge curve — one complete cycle against the new cell lets it rebuild an accurate coulomb count. Skip this and the percentage readout will drift.

Why the Lumia 550 reports wrong battery percentage after a cell swap

The Lumia 550 uses a coulomb-counting fuel gauge IC that tracks charge by integrating current over time against a stored discharge curve. When you swap cells, the IC still references the old cell's curve — so its percentage estimate drifts almost immediately. The fix is one uninterrupted full discharge followed by a full charge with the phone in low-power mode. After that single cycle, the IC writes a new baseline and percentage accuracy returns. If the drift persists after two cycles, check that the battery connector is fully seated — an intermittent contact causes the IC to log false current readings.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff failure — the cell's internal resistance climbs enough that under modem or screen load the voltage drops below the BMS cutoff threshold even though the fuel gauge still shows charge remaining. It happens most often if the replacement cell has been stored for an extended period before installation, leaving it partially discharged. Before fitting the battery, check resting voltage with a multimeter — it should read above 3.6V. If it reads below 3.5V, connect it to a charger for 20 minutes before installation to bring it into the BMS's normal operating window before the phone attempts to calibrate against it.