Saiet BASIC Replacement Battery 3.7V 1200mAh Li-ion

Saiet BASIC / Pronto Max / SCUDOtre+ — 3.7V Li-ion Replacement Battery

This is a 3.7V 1200mAh Li-ion cell for the Saiet BASIC, Pronto Max, and SCUDOtre+ mobile phones. It replaces the original battery when capacity has faded or the cell no longer holds a charge. Physical dimensions are 53.00 × 33.90 × 5.70mm — confirm these against your existing cell before ordering.

• BASIC, Pronto Max, and SCUDOtre+ compatibility: These three models share the same cell footprint, connector pinout, and 3.7V nominal voltage rail, which is why one part number covers all three. The BMS handshake and thermistor line are consistent across the range.
• Bench tested on actual hardware: We cycled this cell through full discharge-charge sequences and monitored BMS cutoff behaviour at both ends of the voltage curve. The protection circuit responded correctly at low-voltage lockout and at charge termination — no anomalous cutoffs mid-cycle.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This allows the fuel gauge IC to recalibrate against the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the Saiet BASIC after a cell swap

This is a voltage cliff problem, not a capacity problem. When the modem transmits or the screen brightness spikes, current draw pulls cell voltage down sharply. If the fuel gauge IC is still calibrated to the old degraded cell's curve, it reads 25% but the new cell's actual terminal voltage has already dropped below the system cutoff threshold — around 3.2V under load. The phone shuts down as a protective response, not because the cell is faulty. Run one full discharge to 3.0V under normal use, then charge to 100% without interruption — this resets the coulomb counter baseline.

Phone not powering on after the replacement cell sat in storage

Li-ion cells self-discharge in storage, and if the cell voltage has dropped below 2.5V, the BMS enters a lockout state to prevent damage. The phone will show nothing — no charging indicator, no boot screen. Connect the phone to a wall charger, not a USB port, and leave it for 15–20 minutes without pressing any buttons. The charge IC needs to trickle current into the cell to lift voltage above the BMS re-enable threshold, which is typically around 2.9–3.0V. Once the charging indicator appears, the BMS has re-initialised and normal charging can proceed.