Lenovo Tab P12 L21C2P31 Replacement Battery 3.87V 10000mAh

Lenovo Tab P12 / TB-370FU — 3.87V Li-Polymer Replacement Battery (L21C2P31)

This is a 3.87V, 10000mAh (38.7Wh) Li-Polymer battery for the Lenovo Tab P12 and Tab P12 2023 tablet. It fits TB-370FU and ZACH0165US units and replaces OEM part numbers L21C2P31, L21D2P31, L21L2P31, L21M2P31, SB18D1S172, and SB18D15171. Install this when the original cell no longer holds a full charge or the tablet shuts off unexpectedly under load.

• Tab P12 series coverage: The TB-370FU board uses a shared connector pinout and BMS handshake voltage across the 2023 Tab P12 lineup. All listed OEM part numbers draw from the same 3.87V nominal cell spec, so one replacement covers multiple unit variants without wiring changes.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a TB-370FU board. The BMS accepted the cell without a protection trip, the charge IC ramped to full current, and voltage held steady within spec across the full discharge curve.
• Fuel gauge reset after installation: After fitting this battery, run the tablet down to automatic shutoff — not a manual power-off — then charge uninterrupted to 100%. This gives the fuel gauge IC a full voltage window to recalibrate against the new cell and eliminates the inaccurate percentage readings that are common after any cell swap.

Lenovo Tab P12 shutting down at 15–25% remaining

This happens when the fuel gauge IC is still calibrated to the old, degraded cell. The percentage shown on screen no longer maps accurately to the actual cell voltage. When the display, Wi-Fi radio, and processor pull current simultaneously, the real cell voltage drops faster than the OS expects and the protection circuit cuts power. One full discharge-to-shutoff cycle followed by an uninterrupted charge to 100% resets the calibration window and resolves the early cutoff. After that cycle, the OS reads the correct voltage floor — typically around 3.40V — before triggering shutdown.

Fast charging not available on the Tab P12 after a battery swap

The Tab P12 uses USB-PD negotiation to unlock higher charge rates. On the first charge after a cell replacement, the charge IC may fall back to standard 5V input while it confirms the new cell is responding within expected parameters. This is not a fault — it resolves after one complete accepted charge cycle. Use the original Lenovo charger and cable for this first cycle, as a third-party charger that doesn't support the correct USB-PD profile will keep the charge rate locked at 5W regardless of how many cycles you run.