Brondi BIGFP600AA Replacement Battery 3.7V 900mAh

Brondi Amico Ampli Vox / Amico Clock Series — 3.7V Li-ion Replacement Battery (BIGFP600AA)

This is a 3.7V, 900mAh Li-ion cell replacing the original battery in the Brondi Amico Ampli Vox, Amico Clock, Amico Fedele, Amico Flip, and over a dozen additional Amico-series handsets. It matches the original 53.00 × 34.00 × 4.30mm footprint and connects via the same OEM connector layout. Rated at 3.33Wh, it restores full call, messaging, and basic phone function to a handset whose original cell has degraded.

• Amico-series platform fit: The Amico lineup shares a common PCB architecture across models — same voltage rail at 3.7V, same physical connector, and a BMS that handshakes identically across the BIGFP600AA, BIGFP800AC, W3, and W11 part numbers. That is why one cell covers such a wide model range.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Amico platform, confirmed BMS handshake without error flags, and verified the charge IC accepted full current without thermal cutoff or premature charge termination.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging if available and run one complete discharge-to-charge cycle. This gives the fuel gauge IC a full reference curve against the new cell before the OS starts interpreting state-of-charge data — without it, percentage readings after a cell swap are unreliable.

Why the Amico Ampli Vox reports wrong battery percentage after a cell swap

The fuel gauge IC on these handsets builds its state-of-charge model by learning the discharge curve of the installed cell over time. When you swap the cell, that learned curve no longer matches the new cell's actual voltage-to-capacity relationship. The IC continues using the old curve, so it reports percentages that do not reflect the new cell's real state. One full discharge from 100% down to automatic shutdown, followed by a full charge without interruption, forces the IC to re-anchor its reference points against the new cell.

Sudden shutdown at 20–30% remaining on the replacement cell

This is a voltage cliff failure — the cell voltage drops sharply under the load of an active call or backlight, falling below the BMS cutoff threshold even though the fuel gauge still reads 20–30%. It is most common when the new cell is still in its first few cycles and the gauge IC has not yet recalibrated. Run two full discharge-charge cycles without interruption, and check that the charge IC reaches 4.2V at the end of each charge. If shutdown continues below 3.6V under load after three full cycles, the cell may have a high internal impedance fault.