About this replacement
Asus E502SA / EeeBook L502MA Series — 7.6V Li-Polymer Replacement Battery (B21N1506)
This 7.6V, 4050mAh (30.78Wh) Li-Polymer battery replaces the original cell in the Asus E502SA and EeeBook L502MA/E502MA series 15.6-inch notebooks. It fits models cross-referenced under OEM part numbers B21N1506, 0B200-01430600, 0B200-01430700, and 0B200-01430800. Install it when the original pack no longer holds a charge or when the system reports battery health as failed.
- E502SA and EeeBook L502MA platform fit: These models share the same 7.6V two-cell Li-Polymer architecture, identical connector pinout, and the same BMS handshake protocol — so one pack covers the full lineup without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an E502SA board. The BMS negotiated correctly on first connection, charge current stepped down as expected at 80%, and the fuel gauge IC accepted the new cell data without a forced reset.
- Post-swap calibration cycle for the E502SA: After installing, run the laptop down to hibernate cutoff on normal use — not by pulling the power — then charge uninterrupted to 100% without using the machine. This resets the BIOS battery learn cycle and clears the inaccurate health flag that fires after every cell replacement on this platform.
Why the E502SA shuts down at 20–30% battery shown on screen
The E502SA uses an Intel Celeron or Pentium N-series processor paired with a 1080p display — both pull hard when the CPU boosts and the backlight is at full brightness. Under that combined load, a degraded or new uncalibrated cell hits a voltage cliff before the fuel gauge reaches zero. The BIOS interprets the sudden voltage drop as a critical low and forces an immediate shutdown regardless of the percentage shown. Running the calibration cycle above lets the fuel gauge IC map the actual discharge curve of the new cell, which eliminates premature cutoffs.
BIOS shows incorrect Wh rating after fitting a new cell
The Wh figure shown in BIOS or Windows Battery Report is read from the battery's EEPROM, not measured live — it reflects the rated chemistry data written into the pack's controller chip. A new cell with a slightly different internal EEPROM revision can report a Wh value that differs from the sticker spec by a small margin. This is not a fault with the battery or the board. Confirm the actual pack voltage reads 7.6V at the connector with a multimeter, then proceed with the calibration cycle — the reported Wh figure stabilises after two to three full charge-discharge passes.