About this replacement
Archos 40b Titanium — 3.7V Li-ion Replacement Battery (AC40bTI)
This is a 3.7V Li-ion cell rated at 1250mAh (4.63Wh), built to the AC40bTI specification. It fits the Archos 40b Titanium and 40b Titanium Surround smartphones. Install it when the original cell no longer holds a charge or causes unexpected shutdowns.
- 40b Titanium and Titanium Surround compatibility: Both variants share the same battery bay dimensions and connector pinout. The 61.51 × 50.07 × 4.40mm cell fits the housing without modification, and the BMS communicates over the same three-pin interface used across the Titanium line.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the 40b Titanium hardware. The BMS accepted the cell without triggering a protection fault, and charge current stepped down correctly at the CV transition.
- Fuel gauge recalibration on first cycle: After installation, disable any fast-charge mode and run one complete discharge-charge cycle before normal use. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.
Why the 40b Titanium reports wrong battery percentage after a cell swap
The fuel gauge IC on the 40b Titanium stores a discharge curve profile for the original cell. When a new cell goes in, that stored profile no longer matches the actual cell chemistry, so the percentage readout drifts. The IC uses a coulomb counter that resets its reference points only after seeing a full discharge and full charge. One complete slow cycle — no fast charge — corrects the calibration and stabilises the percentage display.
Sudden shutdown at 20–30% on the replacement cell
This happens because the modem and display draw a combined current spike the cell cannot sustain at low state-of-charge, causing voltage to dip below the BMS cutoff threshold even though the gauge still shows charge remaining. The fuel gauge IC has not yet learned the new cell's voltage cliff point, so it does not flag low battery in time. Run two full discharge-charge cycles without fast charging to let the IC recalibrate. After calibration, the low-battery warning should trigger before voltage collapses under load.