Simvalley SP-40 Replacement Battery 3.7V 1200mAh PX-3423

Simvalley SP-40 / SP-60 — 3.7V Li-ion Replacement Battery (PX-3423)

This is a 3.7V 1200mAh Li-ion cell for the Simvalley SP-40 and SP-60 smartphones. It replaces OEM part numbers PX-3423 and PX-3423-675. Swap it in when the original cell no longer holds a usable charge or causes unexpected shutdowns.

• SP-40 and SP-60 shared platform: Both handsets run the same 3.7V voltage rail and use an identical physical connector and cell footprint at 63.60 × 40.00 × 4.45mm. The BMS handshake is compatible across both models, so one cell covers the pair.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence on the SP-40 and monitored BMS cutoff behaviour at low voltage. The protection circuit tripped correctly at the low-voltage threshold and accepted a charge without fault flags on the first cycle.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge down to auto-off, then charge to 100% without interruption. This lets the fuel gauge IC map its coulomb counter to the new cell's discharge curve before high-current charging begins.

Why the SP-40 reports wrong battery percentage after a cell swap

The SP-40 uses a fuel gauge IC that stores a learned discharge curve from the original cell. When you fit a new cell, that stored curve no longer matches actual cell behaviour, so the reported percentage drifts from reality. The gauge reads voltage and estimates state-of-charge against old calibration data. One full discharge-charge cycle forces the coulomb counter to reset and relearn against the new cell. After that cycle, percentage readout stabilises.

Sudden shutdown at 20–30% on the SP-40 after replacement

This is a voltage cliff, not a capacity fault. When the modem transmits or the screen hits peak brightness, the cell must deliver a short high-current burst. If the cell voltage sags below the BMS cutoff threshold under that load — even while the gauge still reads 20–30% — the phone shuts off to protect the circuit. Let the phone power back on and check the resting voltage in the battery settings menu; a reading below 3.5V under no-load confirms the cell is discharging non-linearly. Run one full calibration cycle first — if shutdowns persist after that, check that the battery contacts are fully seated and clean.