About this replacement
Acer Chromebook 11 N7 / C731 Series — 11.1V Li-Polymer Replacement Battery (AP16J5K)
This 11.1V, 3950mAh (43.85Wh) lithium-polymer battery replaces the original AP16J5K / AP16J8K cell in the Acer Chromebook 11 N7 and C731 series. It fits a wide range of C731 variants including the C731-C7P9 and C731-C8VE, among others. Same voltage, same connector, same physical footprint at 217.14 × 119.08 × 6.40mm.
- C731 series compatibility: All C731 variants in this family share the same 11.1V power rail, connector pinout, and BMS handshake protocol. One cell covers the full range because Acer standardised the battery interface across this Chromebook line.
- Bench tested on actual hardware: We cycled this cell on a C731 chassis and confirmed the BMS negotiated correctly — charge accepted cleanly from 0%, voltage held stable under combined CPU and display load, and no cutoff faults triggered during deep discharge testing.
- Post-install calibration on ChromeOS: After fitting this cell, let the Chromebook discharge fully until it hibernates on its own, then charge it uninterrupted to 100%. This forces the fuel gauge IC to re-learn the new cell's capacity curve and clears the inaccurate health warning that ChromeOS displays after every cell swap.
Why ChromeOS reports poor battery health immediately after a C731 cell swap
The Chromebook's embedded controller reads health data from EEPROM registers that were written by the original factory cell. When a new cell goes in, those EEPROM values don't match the fresh chemistry, so the OS flags the battery as degraded before a single charge cycle has run. This is a data mismatch, not a fault with the replacement cell. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% triggers the BIOS battery learn cycle and rewrites those registers against the new cell's actual behaviour. After one or two complete cycles, the health indicator normalises.
Chromebook shutting down at 20–30% shown after battery swap
This happens because the fuel gauge IC is still referencing the old cell's voltage-to-capacity curve. Under full CPU and display load, the new cell hits a voltage cliff earlier than the stale curve predicts, and the controller triggers an emergency shutdown to protect the hardware. The fix is calibration, not a faulty cell. Discharge the laptop fully to hibernate cutoff — do not interrupt it — then charge straight to 100%. Repeat this once more if the shutdowns persist; the gauge IC typically stabilises within two full cycles and the cutoff point drops back below 10%.