BP5E Redmi A5 4G Replacement Battery 3.85V 5100mAh

Redmi A5 4G — 3.85V Li-Polymer Replacement Battery (BP5E)

This 3.85V, 5100mAh (19.64Wh) Li-Polymer battery replaces the OEM BP5E cell in the Redmi A5 4G smartphone. It fits the A5 4G directly and restores power to the processor, display, modem, and all onboard functions. Install it when the original cell no longer holds charge or the phone shuts down unexpectedly.

• A5 4G platform fit: The BP5E connector, contact layout, and BMS handshake are specific to the Redmi A5 4G chassis. The replacement cell matches those parameters so the phone's charge IC and fuel gauge IC can communicate with the battery normally.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the A5 4G platform. The BMS accepted the charge IC handshake on the first cycle, and charge current ramped correctly through CC and CV phases without interruption.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current fast charging introduces load the IC hasn't yet measured.

Sudden shutdown at 20–30% on the Redmi A5 4G

A new Li-Polymer cell has a slightly different voltage-to-capacity curve than the cell the fuel gauge IC was originally calibrated to. Under modem or display load, the cell voltage drops faster than the IC expects in that 20–30% window, crossing the BMS cutoff threshold while the OS still shows charge remaining. This is a calibration gap, not a faulty cell. One full discharge to automatic shutdown followed by a complete charge at standard rate resets the coulomb counter and closes that gap.

USB fast charge not activating after battery replacement

The A5 4G's charge IC uses a handshake over the USB-PD or proprietary charge protocol to negotiate fast charge current with the connected adapter. On the first cycle after a cell swap, the BMS on the new cell may not respond to that negotiation until it has completed one standard-rate charge cycle from a low state. If fast charging is absent after installation, charge the phone once from below 10% to 100% using the standard brick — not a fast charger. Fast charge negotiation typically resumes from the second cycle onward.