Dynavox FMP3 Replacement Battery 3.7V 1200mAh Li-ion

Dynavox FMP3 — 3.7V Li-ion 1200mAh Replacement Battery

This is a 3.7V lithium-ion replacement battery rated at 1200mAh (4.44Wh) for the Dynavox FMP3 portable communication device. It fits directly into the FMP3 and restores power to a unit that no longer holds a usable charge. Physical dimensions are 53.00 × 33.90 × 5.70mm — verify against your existing cell before ordering.

• FMP3 platform fit: The FMP3 runs a single-cell 3.7V Li-ion configuration. This cell matches that voltage rail and the physical footprint the device requires. No adapter or modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench with BMS monitoring active. The protection circuit responded correctly to over-voltage and over-discharge thresholds. Charge acceptance was stable across multiple cycles.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging if available and run one complete discharge-to-charge cycle before normal use. This lets the fuel gauge IC map the new cell's discharge curve before it begins reporting percentages under real load conditions.

Sudden shutdown at 20–30% on the FMP3 after a cell swap

This is a voltage cliff issue, not a capacity defect. The fuel gauge IC on the FMP3 was calibrated to the discharge curve of the original aged cell. When the new cell hits a load spike — screen at full brightness, audio output, or wireless transmission — voltage drops faster than the gauge expects at that percentage. The device interprets the sag as a critical low and shuts down before the display reads zero. One full discharge-to-charge cycle recalibrates the coulomb counter against the new cell and eliminates most of these premature shutdowns.

FMP3 not powering on after the replacement cell sat in storage

Li-ion cells self-discharge in storage. If the cell voltage dropped below approximately 2.5V before installation, the BMS trips into deep-discharge lockout and blocks all current flow to protect the cell. The device will show no response — no boot screen, no charging indicator. Connect the FMP3 to a wall charger and leave it for 15–20 minutes without attempting to power it on. The charge IC will trickle current into the cell until it clears the BMS lockout threshold, typically around 3.0V, at which point normal charging resumes.