About this replacement
Asus Q502L Series — 15.2V Li-Polymer Replacement Battery (B41N1341)
This is a 15.2V 4200mAh (63.84Wh) lithium-polymer battery for the Asus VivoBook Q502L notebook. It fits the Q502L, Q502LA, Q502LA-BBI5T12, and Q502LA-BBI5T15. It replaces OEM part numbers B41N1341 and 0B200-00960000.
- Q502L series fit: These models share the same 15.2V four-cell Li-Polymer configuration, connector pinout, and BMS handshake protocol. Swapping between Q502L variants requires no adapter or wiring change — the BMS communicates directly over the same SMBus line used in the original pack.
- Bench tested on actual hardware: We ran this cell on a Q502LA unit and logged the BMS charge cycle from 0% to full. The protection circuit held charge termination cleanly at 17.4V across all four cells and passed thermal monitoring checks without triggering overcurrent cutoff under sustained CPU load.
- First-cycle reset on Q502L: After fitting this battery, run the laptop down to automatic hibernate cutoff, then charge uninterrupted to 100% without using the machine. This forces the BIOS battery learn cycle to reset against the new cell and clears the false "poor health" warning that appears routinely after any cell swap on this platform.
Why the Q502L shuts down at 20–30% after a battery swap
The Q502LA's BIOS tracks battery voltage curves built around the original cell's discharge profile. A new cell has a slightly different voltage-to-capacity curve, so the fuel gauge IC reads the remaining charge incorrectly at higher load states. When the CPU and display draw full power simultaneously, actual cell voltage drops below the BIOS shutdown threshold before the gauge reaches zero. Running two or three full discharge-to-hibernate cycles recalibrates the fuel gauge IC against the new chemistry and eliminates the early cutoff.
BIOS reporting the replacement battery's Wh rating as wrong
The Wh figure shown in BIOS or Windows Battery Report pulls from EEPROM data embedded in the battery pack — not from a live measurement. If the EEPROM value in the new cell differs from the original pack's rated Wh, BIOS will display a different number even when the actual chemistry is correct. This is a data mismatch, not a capacity fault. Confirm the voltage reads 15.2V and the cell charges to full — those are the functional checks that matter, not the EEPROM Wh label.