Saiet BASIC Replacement Battery 3.7V 900mAh Li-ion

Saiet BASIC Series — 3.7V Li-ion Replacement Battery

This is a 3.7V 900mAh Li-ion cell for the Saiet BASIC, FOCUS VOL, Like Pronto, Prime, and two additional compatible models. It replaces an original cell that no longer holds a useful charge. Voltage and physical dimensions — 53.00 x 34.00 x 4.80mm — match the OEM specification.

• BASIC and FOCUS VOL platform fit: These models share the same battery bay geometry and 3.7V single-cell supply rail. One cell covers all listed variants — no connector adapter or physical modification needed.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence and monitored BMS cutoff behaviour. The protection circuit tripped correctly at the low-voltage threshold and resumed charge acceptance without fault.
• Fuel gauge recalibration on first cycle: After fitting this cell, disable fast charging and run one complete discharge down to automatic shutoff, then charge uninterrupted to 100%. This gives the fuel gauge IC one full cycle to map the new cell's discharge curve before the OS starts reporting accurate percentages.

Why the Saiet BASIC reports wrong battery percentage after a cell swap

The fuel gauge IC on the BASIC stores a learned discharge curve from the previous cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the fresh 900mAh cell. The OS reads state-of-charge from the IC, not directly from cell voltage, so the percentage shown is based on stale calibration data. One full discharge-charge cycle overwrites the old curve and brings the readout back into alignment.

Sudden shutdown at 20–30% on the replacement cell

A freshly installed cell has higher internal impedance than a broken-in one. When the modem transmits or the screen brightness spikes, current draw causes a brief voltage sag that drops below the BMS cutoff threshold — even though the displayed percentage still reads 20–30%. The phone interprets the voltage drop as cell depletion and shuts down. After two to three full discharge-charge cycles, internal impedance drops and the sag narrows; the shutdowns typically stop without any further action.