About this replacement
Apple MacBook Air 13" A1237 / A1304 — 7.4V Li-Polymer Replacement Battery (A1245)
This is a 7.4V, 5400mAh (39.96Wh) Li-Polymer cell replacement for the Apple MacBook Air 13" A1237, A1304, Z0FS, and MB003 series laptops. It replaces OEM part numbers A1245, 661-5196, 661-4915, and 661-4587. The battery sits in the lower case cavity and connects via Apple's proprietary flex connector on the logic board.
- A1237 and A1304 compatibility: Both chassis revisions use the same connector pinout, BMS handshake protocol, and 7.4V nominal rail — the A1245 cell fits both without modification or adapter.
- Bench tested on actual hardware: We ran this cell on an A1304 logic board and confirmed the BMS handshake completed correctly, SMC accepted the battery as a known cell, and charge current stepped down at the expected 4.2V per-cell ceiling.
- First-cycle discharge after installation: After fitting this cell, run the MacBook Air down to automatic hibernate cutoff — do not force shutdown — then charge uninterrupted to 100%. This resets the SMC battery learn cycle and clears the inaccurate health warning macOS logs after every cell swap.
Why macOS reports poor battery health immediately after fitting a new A1245 cell
The MacBook Air stores cumulative cycle count and health data in EEPROM on the battery's protection circuit board. When a new cell arrives, that EEPROM data does not match the charge history macOS expects to see. The System Management Controller reads the mismatch and flags the battery as degraded before it has run a single cycle. One full discharge-to-hibernate followed by an uninterrupted charge to 100% allows the SMC to write a fresh baseline — the health warning clears after one to three calibration cycles.
MacBook Air shuts down at 20–30% charge shown on the menu bar gauge
This happens when the fuel gauge IC still holds calibration data from the old, degraded cell. Under combined CPU and display load, the new cell's actual voltage hits the SMC's low-voltage cutoff while the gauge still reads 20–30% — the two are out of sync. The fix is the same calibration cycle: discharge fully to hibernate, then charge to 100% without interruption. After two to three full cycles the fuel gauge IC recalibrates against the new cell's actual capacity curve and the premature shutdown stops.