About this replacement
Asus Zenpad Z8 / ZenPad 3 8.0 — 3.85V Li-Polymer Replacement Battery (C11PP91)
This is a 3.85V, 4550mAh Li-Polymer battery for the Asus Zenpad Z8, ZenPad 3 8.0, and related variants including the P008 and ZT581KL. It replaces OEM part numbers C11PP91, M619, C11P1514, and 0B200-01970000. Swap it in when the original cell no longer holds charge or causes unexpected shutdowns.
- Zenpad Z8 and ZT581KL platform fit: These models share the same 3.85V power rail, physical footprint, and BMS handshake protocol — 104.20 × 95.80 × 2.70mm cell with matching connector and protection circuit. One battery covers the full variant range.
- Bench tested on actual hardware: We ran this cell through full charge and load cycles on the ZT581KL. The BMS negotiated charge termination correctly at 4.35V and held cutoff at the low-voltage threshold without false trips under display-plus-WiFi combined draw.
- Fuel gauge recalibration after swap: After installing this battery, run the tablet down to automatic shutoff under normal use — no forced discharge needed — then charge uninterrupted to 100%. This resets the fuel gauge IC against the new cell's actual capacity curve and clears the inaccurate percentage reading that appears after any cell swap.
Zenpad Z8 shutting down at 15–25% remaining
This happens when the fuel gauge IC is still calibrated to the old, degraded cell. The reported percentage no longer maps to actual cell voltage. Under combined display and WiFi load, real cell voltage drops faster than the gauge tracks, and the BMS triggers a hard cutoff before the percentage reaches zero. One complete discharge-to-shutoff followed by an uninterrupted charge to 100% resyncs the gauge to the new cell. After that cycle, shutdowns should align with low-battery warnings at or below 5%.
Fast charging not available after battery replacement
The Zenpad Z8 charge IC uses a USB-PD negotiation handshake that can reset to standard 5V charging after a battery swap. This is a firmware-level behaviour — the charge controller defaults to a safe baseline until it completes one full accepted charge cycle on the new cell. Plug in using the original charger and cable, let it charge uninterrupted to 100% without unplugging mid-cycle. After that first complete cycle, fast charge negotiation typically resumes on the next plug-in.