BLU Advance 4.0 M Compatible Battery 3.7V 1200mAh C615044130L

BLU Advance 4.0 M / A090L / A090U — 3.7V Li-ion Replacement Battery (C615044130L)

This is a 3.7V, 1200mAh Li-ion replacement battery for the BLU Advance 4.0 M smartphone, covering model numbers A090L and A090U. OEM part number C615044130L. It fits directly into the original battery bay with no modification required.

• A090L and A090U compatibility: Both variants share the same physical footprint, connector pinout, and 3.7V nominal voltage rail. The BMS handshake protocol is consistent across the A090 series, so one cell covers both regional variants without firmware conflict.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the A090 platform. The BMS accepted the new cell without a protection trip, and the charge IC applied the correct taper current through the CV phase.
• Fuel gauge recalibration on first use: After installation, disable any fast-charge mode and run one complete discharge-to-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before operating under screen or modem load — skipping this step is the main reason percentage readings drift on replacement cells.

Why the Advance 4.0 M reports wrong battery percentage after a cell swap

The fuel gauge IC on the A090 platform stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The gauge reads voltage and maps it against the old data, so percentage shown on screen can be off by 10–20%. One full discharge down to auto-shutdown, followed by an uninterrupted charge to 100%, resets the coulomb counter and lets the IC relearn the new curve. After that cycle, the percentage display stabilises.

Sudden shutdown at 20–30% remaining on the replacement cell

This is a voltage cliff issue, not a capacity problem. When the modem transmits or the screen peaks brightness, instantaneous current draw spikes and the cell voltage dips sharply. If the resting voltage is already near the lower knee of the discharge curve, that spike pulls voltage below the BMS cutoff threshold — around 3.0V — and the phone shuts off even though the gauge shows charge remaining. Letting the phone rest for 30 seconds and powering it back on often shows 15–25% still available. The fix is completing the fuel gauge recalibration cycle so the OS cuts load before the cell reaches that voltage cliff.