About this replacement
Asus VivoBook 14 A420UA Series — 7.7V Li-Polymer Replacement Battery (0B200-03200000)
This 7.7V, 4900mAh (37.73Wh) lithium-polymer cell replaces the original battery in the Asus VivoBook 14 A420UA, A420UA-EK115T, F420UA, and Pro 14 R459UA, plus over 60 additional A420 and F420 variants. It matches the original connector, cell count, and BMS handshake required by the A420UA motherboard. Dimensions are 183.80 × 135.30 × 5.00mm — a direct physical match to the OEM tray.
- A420UA and F420UA platform compatibility: These models share the same two-cell Li-Polymer configuration, 7.7V nominal rail, and C21N1819 BMS protocol. The replacement cell communicates correctly with the EC firmware on all listed variants without triggering a hardware mismatch error.
- Bench tested on actual hardware: We ran this cell on an A420UA-EK115T under simultaneous CPU and display load. The BMS held the 7.7V rail steady through charge and discharge cycles, with thermal cutoff activating correctly at the upper limit. No false low-battery shutdowns occurred during testing.
- Post-swap battery learn cycle: After fitting this cell, run a full discharge to hibernate cutoff, then charge uninterrupted to 100% without using the laptop. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears on the first boot after any cell replacement.
BIOS reporting poor battery health immediately after fitting a new cell
The A420UA stores battery health data in EEPROM on the embedded controller. When a new cell goes in, the EC reads the blank or mismatched EEPROM values and flags the battery as degraded — even though the cell is new. This is not a fault with the replacement. One full discharge-to-hibernate followed by an uninterrupted charge to 100% rewrites the learn cycle data. After two to three full cycles, the BIOS health indicator should read normal.
Laptop shutting down at 20–30% shown on the fuel gauge
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. The IC still maps voltage thresholds from the old, degraded cell — so it miscalculates the remaining capacity and triggers a shutdown well before the cell is actually empty. The fix is to complete two to three full discharge-to-hibernate and uninterrupted full-charge cycles. After calibration, the gauge tracks correctly and shutdowns stop occurring above the true low-voltage cutoff, around 6.0V under load.