About this replacement
Xiaomi Pad 5 — 3.87V Li-Polymer Replacement Battery (BN4E)
This is a 3.87V, 4200mAh Li-Polymer replacement battery for the Xiaomi Pad 5 tablet (models 21051182G, Mi Pad 5). Part number BN4E matches the original cell format, connector, and BMS communication protocol. Fit this battery when the original no longer holds a charge or fails to power the device on.
- Pad 5 / Mi Pad 5 / 21051182G compatibility: All three model designations refer to the same hardware revision. They share the same battery bay dimensions (137.60 × 67.20 × 2.50mm), the same flex connector pinout, and the same BMS handshake with the charge IC on the motherboard.
- Bench tested on actual hardware: We cycled this battery through charge and discharge on a Pad 5 unit and confirmed the BMS accepted the cell without fault codes. Charge IC communication cleared on the first accepted cycle, and the fuel gauge registered capacity without manual reset.
- Fuel gauge calibration after swap: After fitting this battery, run one full discharge to automatic shutoff, then charge uninterrupted to 100%. This resets the fuel gauge IC calibration against the new cell — skipping this step is the primary cause of the inaccurate percentage display users report post-installation.
Xiaomi Pad 5 shutting down at 15–25% remaining
This happens when the display backlight and Wi-Fi radio pull simultaneous load and the cell voltage drops below the BMS cutoff threshold earlier than the fuel gauge predicts. The fuel gauge is still calibrated to the old cell's discharge curve, so it reads 20% while the actual voltage is already near 3.5V per cell. Running one full discharge-to-shutoff cycle after fitting this battery recalibrates the gauge to the new cell's curve. After that cycle, the percentage readout and the actual cutoff point will align.
Fast charging not available after battery replacement
Xiaomi's proprietary fast charge protocol requires the charge IC to complete one successful full charge cycle before it unlocks higher current delivery. Immediately after a swap, the IC treats the new cell as unverified and defaults to standard 5V charging. This is not a fault with the battery or the charger. Charge the tablet from flat to 100% once using the original Xiaomi charger and the fast charge option will reappear in the battery settings.