Archos 40 Cesium Replacement Battery 3.8V 1950mAh

Archos 40 Cesium — 3.8V Li-ion Replacement Battery

This 3.8V, 1950mAh Li-ion cell replaces the original battery in the Archos 40 Cesium smartphone. It fits the compact 40 Cesium body at 58.50 x 50.95 x 5.40mm. Capacity figures are taken from the product specification — 7.41Wh total energy.

• Archos 40 Cesium fit: The 40 Cesium uses a fixed 3.8V nominal rail matched to its charging IC and modem power supply. This cell matches that rail and the physical footprint exactly — no connector adaptation needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the 40 Cesium platform. The BMS accepted charge at standard 1C rate without tripping overcurrent protection, and the fuel gauge IC tracked state of charge without error flags on the first full cycle.
• First-cycle fuel gauge reset: On first use after fitting, disable any fast-charge mode and run one complete discharge down to automatic shutoff, then charge uninterrupted to 100%. This gives the fuel gauge IC one clean reference curve against the new cell before high-current charging pushes current into an uncalibrated counter.

Why the 40 Cesium reports wrong battery percentage after a cell swap

The Archos 40 Cesium uses a coulomb-counting fuel gauge IC that builds its state-of-charge model from learned discharge curves. When you swap in a new cell, that learned model no longer matches the new cell's actual voltage-to-capacity curve. The gauge may show 80% remaining while the real cell voltage is already near cutoff. One full uninterrupted discharge-charge cycle forces the IC to rewrite its reference table against the new cell. After that cycle, percentage readouts stabilise to within a few percent of actual state of charge.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff symptom, not a capacity problem. Under modem transmit load or screen brightness spikes, the cell voltage drops sharply at lower states of charge — faster than the fuel gauge IC expects. The phone's protection circuit reads that dip as a hard undervoltage event and cuts power before the displayed percentage reaches zero. Run that first full calibration cycle and check that the charge termination voltage reaches 4.35V. If shutdowns persist past two full cycles, measure resting cell voltage at reported 25% — it should read above 3.6V.