Saiet Magnum Due Replacement Battery 3.7V 1300mAh Li-ion

Saiet Magnum Due — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1300mAh Li-ion replacement battery for the Saiet Magnum Due smartphone. It slots into the original battery bay and restores power to devices where the original cell has degraded through repeated charge cycles. Capacity is 4.81Wh as measured against the product specification.

• Magnum Due fit: The Magnum Due uses a compact 60.00 × 43.80 × 4.50mm cell with a 3.7V nominal rail. This replacement matches those dimensions and voltage exactly — the connector seats flush and the BMS handshake completes on first boot without requiring any manual pairing step.
• Bench tested on actual hardware: We cycled this cell through a full discharge and recharge on the bench. The BMS held charge cutoff at the correct upper threshold and did not trigger an over-voltage fault. Load response during the simulated call and screen-on draw stayed stable across the full discharge curve.
• Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. The Magnum Due's fuel gauge IC is calibrated to the old cell's discharge curve. Running one full cycle at standard charge rate lets the coulomb counter map the new cell before high-current charging is applied to an uncalibrated reference.

Sudden shutdown at 20–30% on the Magnum Due after a cell swap

This is a voltage cliff issue, not a capacity fault. When the modem transmits or the screen drives peak backlight, current draw spikes sharply. A new cell with a slightly different internal resistance curve can drop below the BMS cutoff voltage under that load even while the fuel gauge still reads 20–30%. The phone interprets the voltage drop as a hard shutdown threshold, not a capacity reading. One full discharge-to-shutdown cycle followed by an uninterrupted charge to 100% forces the fuel gauge IC to re-anchor its low-voltage reference to the new cell.

Battery percentage jumping erratically after fitting the replacement

Erratic percentage readings mean the coulomb counter is still using the discharge model from the original cell. The Magnum Due's fuel gauge IC does not auto-reset when a new battery is detected — it resumes counting from wherever the old model left off. The fix is a single full discharge run down to automatic shutdown, then a full uninterrupted charge to 100% with the screen on to keep the device awake through the calibration cycle. After one complete cycle the percentage display stabilises and tracks the actual remaining charge correctly.