Olympia Janus 3.7V Replacement Battery 1000mAh Li-ion

Olympia Janus — 3.7V Li-ion 1000mAh Replacement Battery

This is a 3.7V Li-ion cell rated at 1000mAh (3.7Wh) for the Olympia Janus smartphone. It fits directly into the Janus battery bay and connects via the original ribbon contact. Voltage and physical dimensions — 47.10 x 44.00 x 5.50mm — match the OEM specification.

• Olympia Janus fit: The Janus uses a slim 5.50mm profile cell at 3.7V. This replacement matches that profile exactly. The BMS trips on overvoltage, so a mismatched cell will prevent the device from booting — voltage match matters here.
• Bench tested on actual hardware: We cycled this cell through charge and load, monitoring BMS cutoff thresholds at both ends. The protection circuit engaged cleanly at the low-voltage floor, and charge termination fired at full capacity without overrun.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its discharge curve against the new cell before high-current charging pushes current into an uncalibrated state.

Sudden shutdown at 20–30% on the Olympia Janus

This happens when the fuel gauge IC is still calibrated to the old cell's discharge curve. The new cell hits a voltage cliff under modem or screen load before the reported percentage reaches zero. The phone cuts out because actual cell voltage drops below 3.2V even though the OS thinks charge remains. One full discharge-to-cutoff followed by an uninterrupted charge cycle forces the coulomb counter to re-anchor to the new cell's actual capacity.

OS reporting wrong battery percentage after cell swap

The Janus stores historical discharge data in the fuel gauge IC, and that data does not reset automatically when the cell is swapped. The IC interpolates percentage from a curve that no longer matches the new cell. This causes jumpy readings — often reporting 100% immediately after install, then dropping sharply. Drain the battery until the phone shuts off on its own, then charge to full without interruption to reset the calibration baseline.