About this replacement
Asus P2520LJ / PU551LA Series — 14.4V Li-ion Replacement Battery (A41N1421)
This 14.4V Li-ion battery replaces the original cell in the Asus P2520LJ, PU551LA, P2520SA, and ZX50JX4200, along with several hundred compatible variants sharing the same connector and BMS handshake. Capacity is 2400mAh (34.56Wh), matching the stock specification. It covers the A41N1421 OEM part number and cross-references including 0B110-00320100, 0B110-00280000, and related variants.
- P2520 and PU551 platform fit: These models share a four-cell Li-ion architecture on the same 14.4V rail with an identical locking connector and BMS communication protocol — which is why one cell works across all of them without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the P2520LJ platform. The BMS handshook correctly with the Asus EC, reported accurate state-of-charge to the OS, and thermal cutoffs triggered at expected thresholds during load testing.
- Post-install calibration on P2520 series: After fitting this cell, run the laptop down to automatic hibernate cutoff — do not manually shut down — then charge uninterrupted to 100% without use. This resets the BIOS battery learn cycle and clears the false "poor health" warning that appears after any cell swap on this platform.
Why the P2520LJ BIOS reports poor battery health on a new cell
The Asus EC reads health data from EEPROM registers populated by the previous cell's charge history. When a new cell goes in, those registers still hold the old degraded-cell values, so the BIOS flags the new battery as worn before it has run a single cycle. This is firmware behaviour, not a fault with the replacement. Running one full discharge-to-hibernate then an uninterrupted charge to 100% forces the EC to rewrite the learn cycle data against the new cell. After one or two cycles, the health indicator normalises.
Laptop shuts off at 20–30% remaining after the battery swap
The fuel gauge IC calibrates its empty-point estimate against the previous cell's internal resistance profile. With a new cell installed, the IC underestimates remaining capacity and triggers a low-voltage shutdown too early — typically between 20% and 30% displayed charge. The cell voltage at that point is still well above the actual cutoff floor. Perform two full discharge-to-hibernate cycles followed by full uninterrupted charges; the fuel gauge IC recalibrates its curve against the new cell's chemistry, and the shutdown threshold returns to near 0%. After the second cycle, the displayed percentage at shutdown should be below 5%.