SNN5681 Motorola MPX200 Replacement Battery 3.7V 750mAh

Motorola MPX200 — 3.7V Li-ion Replacement Battery (SNN5681)

This is a 3.7V, 750mAh lithium-ion cell built to the SNN5681 specification. It fits the Motorola MPX200 smartphone. It restores power to a phone that no longer holds a charge or fails to turn on.

• MPX200 platform fit: The MPX200 uses a single-cell 3.7V Li-ion pack with a specific connector pinout and BMS communication line. This cell matches that pinout and voltage rail, so the phone's charge IC recognises it without throwing a charge fault.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the MPX200 platform. The BMS accepted the cell on first connection, charge termination triggered correctly at 4.2V, and the low-voltage cutoff engaged without locking the board.
• Fuel gauge recalibration on first use: After installing this cell, disable any fast-charge mode for the first full discharge-charge cycle. This gives the MPX200's fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Why the MPX200 reports wrong battery percentage after a cell swap

The MPX200's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the new cell's actual voltage-to-capacity relationship. The phone reads voltage and translates it to a percentage using the old map, so the number on screen drifts. One full discharge down to auto-shutoff, followed by a full uninterrupted charge to 100%, forces the IC to rewrite its reference curve against the new cell.

Sudden shutdown at 20–30% on the MPX200

This happens when the cell voltage drops sharply under load — modem transmit bursts and screen backlight draw current simultaneously, and a weakened or miscalibrated cell cannot hold voltage above the BMS cutoff threshold. The phone shuts off even though the reported percentage looks safe. The fuel gauge is reading average resting voltage, not the sag under peak load. Run one full calibration cycle first; if shutdowns continue, check that the cell contact tabs are fully seated — a loose connection raises internal resistance and worsens voltage sag under load.