BL-61CT KOOBEE S3 Replacement Battery 3.8V 2000mAh Li-ion

KOOBEE S3 / S100 / M100 — 3.8V Li-ion Replacement Battery (BL-61CT)

This is a 3.8V, 2000mAh Li-ion battery rated at 7.6Wh, carrying OEM part number BL-61CT. It fits the KOOBEE S3, S100, and M100 smartphones. These three models share the same battery bay dimensions and connector, so one cell covers all three.

• S3, S100, and M100 compatibility: All three models use the same physical footprint — 75.43 × 54.94 × 3.95 mm — the same flex connector pinout, and the same BMS handshake protocol. One replacement cell works across the entire range without modification.
• Bench tested on actual hardware: We ran BL-61CT cells through charge and discharge cycles on compatible hardware. The BMS accepted the cell without triggering fault flags, and the charge IC brought voltage up from rest to full-charge termination without cutoff interruption.
• 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 build an accurate discharge curve against the new cell before high-current charging pushes current into an uncalibrated state register.

Sudden shutdown at 20–30% on the BL-61CT replacement cell

An aged original cell loses capacity gradually, and the fuel gauge IC calibrates its percentage readings to that degraded curve. When a fresh 2000mAh cell goes in, the IC still references the old curve. Under modem transmission or screen-on load, the phone hits a voltage cliff the IC did not anticipate and cuts power. One full uninterrupted discharge-to-shutdown followed by a full charge corrects the coulomb counter reference. After that cycle, shutdowns at 20–30% should stop.

Device will not power on after BL-61CT sat discharged in storage

Li-ion cells discharged below 2.5V per cell trigger a BMS lockout — the protection circuit opens and the phone sees no voltage at all. Plugging in a standard charger does nothing because the charge IC needs a minimum rail voltage to start. Connect to a wall adapter rated at 5V/1A and leave it for 15–20 minutes without pressing the power button — the charge IC will trickle current through the BMS lockout threshold. Once cell voltage recovers above 2.7V, the BMS resets and normal charging resumes.