Sagem MY600x Replacement Battery 3.7V 1000mAh Li-ion

Sagem MY600x / MY800x Series — 3.7V Li-ion Replacement Battery (189247961)

This is a 3.7V, 1000mAh Li-ion cell for the Sagem MY600x, MY600v, MY800x, and MY800v mobile phones. It replaces OEM part numbers 189247961, 252822138, SOIA-SN1, and SO1B-SN1. The battery slots into the rear compartment and connects through the original contact plate.

• MY600 and MY800 series fit: Both series share the same battery bay dimensions (59.84 × 36.55 × 4.40mm), contact layout, and voltage rail, so one cell covers all four confirmed models without modification.
• Bench tested on actual hardware: We cycled this cell through the Sagem charge IC and confirmed the BMS communicated correctly — charge current tapered at full capacity and the protection circuit tripped cleanly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: After fitting this cell, run one uninterrupted discharge to auto-shutdown, then charge to 100% without interruption. The Sagem fuel gauge IC maps its percentage readings against the cell's discharge curve on this first full cycle — skipping it causes erratic percentage jumps for the first several days.

Sudden shutdown at 15–25% on the Sagem MY600x

The MY600x fuel gauge IC was calibrated against the original cell's discharge curve at the factory. A new cell has a slightly different internal resistance profile, so the IC misjudges where the voltage cliff sits. When the modem fires during a call or data burst, current draw spikes and cell voltage drops faster than the gauge predicted. The phone interprets this as an immediate undervoltage condition and shuts down — even though the displayed percentage still read 20% or higher. One full discharge-charge cycle lets the IC recalibrate and shifts the predicted cutoff point to match the actual cell.

Phone won't power on after the battery sat in storage

Li-ion cells self-discharge in storage at roughly 2–3% per month. If this battery shipped or was stored for an extended period, cell voltage may have dropped below 3.0V. At that point the BMS locks out charging to protect against lithium plating on a deeply discharged anode. Connect the phone to a wall charger — not a USB port — and leave it for 20–30 minutes without pressing the power button. The charge IC applies a trickle current to recover the cell above the 3.0V reinitialisation threshold, after which normal charging resumes.