About this replacement
Acer Nitro 5 AN517-55 / Predator Helios 300 PH317-56 — 15.4V Li-ion Replacement Battery (AP21A7T)
This is a 15.4V 5650mAh (87.01Wh) Li-ion battery for the Acer Nitro 5 AN517-55 series and Predator Helios 300 PH317-56 series laptops. It replaces OEM part numbers AP21A7T, AP21A8T, and KT0040G014. Install it when the original cell no longer holds charge or swells under the chassis.
- Nitro 5 and Helios 300 shared platform: These models share the same 15.4V four-cell architecture, connector pinout, and BMS handshake protocol — one cell fits both lines without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Nitro 5 AN517-55 chassis. The BMS communicated correctly with the EC, reported accurate state-of-charge data, and balanced across all four cells without triggering a fault code.
- Post-install calibration on Nitro 5: After fitting, run the laptop down to hibernate cutoff under normal load — gaming or a CPU stress test works — then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap.
Why the Nitro 5 shuts down at 20–30% remaining after a battery swap
The Nitro 5 EC uses a fuel gauge IC to estimate remaining capacity based on learned discharge curves from the previous cell. After swapping to a new cell, those curves are stale. Under full CPU plus display load the voltage drops faster than the old model predicts, and the EC triggers a shutdown before the cell is actually empty. Run two full discharge-to-hibernate cycles under load to let the gauge IC rebuild its curve against the new cell's actual chemistry.
BIOS reporting the new battery as unknown or 0% after installation
This happens because the BIOS reads EEPROM data written to the old cell — manufacturer ID, cycle count, and design capacity — and flags a mismatch when it finds a fresh cell. It is not a fault with the replacement. Boot into the BIOS, navigate to the battery information screen, and confirm the voltage reads between 15.0V and 15.4V. If it does, exit and let Windows run a full charge cycle — the health status corrects itself once the fuel gauge IC logs its first complete charge event on the new cell.