About this replacement
Xiaomi Mi Pad 4 Plus — 3.8V Li-Polymer Replacement Battery (BN80)
The BN80 is a 3.8V 8400mAh (31.92Wh) lithium-polymer cell for the Xiaomi Mi Pad 4 Plus tablet. It replaces the original pack when capacity has faded or the battery no longer holds a charge. This part restores the tablet to its factory power spec without modifying the existing charge IC or connector.
- Mi Pad 4 Plus fitment: The BN80 is specific to the Mi Pad 4 Plus — not the standard Mi Pad 4. Both tablets share a similar footprint but use different cell dimensions (154.40 × 117.00 × 2.90mm here) and different BMS handshake parameters. Installing the wrong cell can cause immediate charge IC rejection.
- Bench tested on actual hardware: We cycled the BN80 through charge and discharge on the Mi Pad 4 Plus mainboard. The BMS accepted the cell without fault flags, and the charge IC reached full voltage without thermal events or negotiation errors.
- Fuel gauge recalibration after swap: After installation, run the tablet down to automatic shutoff, then charge uninterrupted to 100% without using the device. This gives the fuel gauge IC one complete cycle against the new cell and corrects the inaccurate percentage readings that almost always appear after a battery swap.
Why the Mi Pad 4 Plus shuts down at 15–25% remaining
The Mi Pad 4 Plus runs a large display alongside Wi-Fi and background sync simultaneously. That combined load pulls enough current to cause a rapid voltage sag in a degraded or freshly swapped cell. The BMS interprets that sag as a critically low voltage event and triggers a protective shutdown before the percentage indicator catches up. After completing one full recalibration cycle, the fuel gauge maps the new cell's discharge curve correctly and the early shutdowns stop.
Fast charging not available after fitting the BN80
Xiaomi's fast charge protocol requires at least one completed charge cycle before the charge IC fully negotiates with a new cell. If fast charging shows as unavailable immediately after installation, that is expected behaviour — not a fault with the battery or the charger. Use the original Xiaomi charger and cable, let the first charge complete fully without interruption, and fast charge will be available on the next session. Using a third-party charger for the first cycle can prevent the protocol handshake from completing correctly.