About this replacement
Archos 40 Neon — 3.7V Li-ion Replacement Battery (AC40NE)
This is a 3.7V, 1200mAh Li-ion battery for the Archos 40 Neon smartphone (OEM part AC40NE). It fits directly into the 40 Neon and restores power to calls, messaging, and apps when the original cell has degraded or failed. Dimensions are 89.92 × 33.40 × 4.50mm — verify clearance before ordering if your unit has been previously repaired.
- Archos 40 Neon compatibility: The 40 Neon uses a dedicated connector and BMS handshake tied to the AC40NE part number. Swapping in a generic cell with the wrong BMS profile can cause the fuel gauge IC to misreport state-of-charge from the first boot.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the 40 Neon platform. The BMS accepted the cell without triggering fault flags, and the charge IC reached termination current cleanly at 4.2V.
- First-cycle fuel gauge recalibration: On first use after installation, disable fast charging if your charging source supports it, then run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Why the 40 Neon reports wrong battery percentage after a cell swap
The Archos 40 Neon uses a fuel gauge IC that builds its state-of-charge model from the original cell's discharge curve. When a new cell goes in, the IC still references the old curve. The result is percentage readings that can be off by 10–20% until the IC recalibrates. One complete discharge down to automatic cutoff, followed by a full charge to 4.2V, resets the coulomb counter against the new cell's actual capacity.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell's voltage drops sharply under load — the modem transmitting or the screen at full brightness — faster than the fuel gauge IC predicted. The phone shuts off not because the battery is empty, but because voltage sagged below the BMS cutoff threshold before the reported percentage reached zero. It is most common in the first few cycles on a new cell. Running two or three full discharge-charge cycles at standard rate lets the fuel gauge IC tighten its voltage-to-percentage mapping and eliminates most of these early shutdowns.