Asus Fonepad 8 Dual Sim C11P1331 Replacement Battery 3.8V 3900mAh

Asus Fonepad 8 Dual Sim — 3.8V Li-Polymer Replacement Battery (C11P1331)

This 3.8V, 3900mAh lithium-polymer battery replaces the C11P1331 cell in the Asus Fonepad 8 Dual Sim and FE380CG. It fits the 8-inch tablet directly, matching the original connector, voltage rail, and form factor. Capacity is sourced from the product specification — 3900mAh at 14.82Wh.

• FE380CG platform fit: The Fonepad 8 Dual Sim and FE380CG share the same charge IC interface and connector pinout. The C11P1331 cell format — 100.90 x 98.40 x 2.70mm — seats flush in both variants without modification to the battery bay or connector housing.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on FE380CG hardware. The BMS accepted the charge IC handshake cleanly from the first cycle, with no voltage irregularities or cutoff events during normal display-plus-WiFi load testing.
• Fuel gauge reset after installation: After fitting this cell, run the tablet down to automatic shutoff — do not force-power it off — then charge uninterrupted to 100%. This gives the fuel gauge IC a full reference window against the new cell and eliminates the inaccurate percentage readings that appear immediately after a swap.

Fonepad 8 shutting down at 15–25% remaining after battery replacement

This happens because the fuel gauge IC is still mapped to the voltage curve of the old, degraded cell. The new cell holds a higher voltage at low state-of-charge than the old one did, so the IC interprets a mid-range voltage as critically low and triggers shutdown. It is not a fault in the replacement battery. One complete discharge-to-shutoff followed by an uninterrupted charge to 100% recalibrates the IC against the actual voltage curve of the new cell. After that cycle, shutdowns at 15–25% typically stop.

Fast charging not available on the Fonepad 8 after a battery swap

The Fonepad 8 charge controller runs a negotiation step at the start of each charge session that can reset after a new cell is installed. If fast charge is not offered on the first charge, complete one full standard charge cycle from low to 100%. The controller re-establishes its baseline on the second cycle and typically resumes the faster charge rate from that point. If the charger output is below 5V/2A, the device will never enter fast charge regardless of battery state — confirm the adapter spec first.