Xiaomi Redmi 5A BN34 Replacement Battery 3.85V 2900mAh

Xiaomi Redmi 5A / M5A — 3.85V Li-Polymer Replacement Battery (BN34)

This is a 3.85V, 2900mAh Li-Polymer replacement battery for the Xiaomi Redmi 5A and M5A smartphones. It uses OEM part number BN34 and slots into the same physical bay as the original cell. Capacity is 11.17Wh — matching the factory specification from the product data.

• Redmi 5A and M5A compatibility: Both model designations share the same chassis, connector pinout, and BMS handshake protocol. One battery covers both variants — no hardware differences affect fitment.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Redmi 5A unit. The BMS accepted the cell without error flags, and the fuel gauge IC initialised correctly after one full cycle.
• Fuel gauge recalibration on first use: After installation, disable fast charging and complete one full discharge-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before the charge IC pushes higher current into an uncalibrated cell.

Sudden shutdown at 20–30% on the Redmi 5A after a cell swap

The Redmi 5A's fuel gauge IC carries its coulomb counter calibration from the old cell. A new cell has a different discharge curve, so the IC underestimates how quickly voltage drops under load — typically from the modem transmitting or the screen at full brightness. When real cell voltage hits the hardware cutoff threshold, the phone shuts down even though the OS still shows charge remaining. One complete discharge to near-zero followed by a full charge resets the coulomb counter against the new cell's actual curve. After that cycle, the reported percentage tracks real voltage correctly.

Phone not powering on after the BN34 sat in storage

Li-Polymer cells self-discharge during storage. If the BN34 dropped below approximately 2.5V per cell before installation, the BMS enters lockout mode and blocks charge current to prevent plating damage. The phone will not power on and will show no charge indicator. Connect to a wall adapter — not a PC port — and leave it for 20–30 minutes without pressing the power button. Most BMS units exit lockout once trickle current from the adapter raises cell voltage above 2.8V, after which normal charging resumes.