Sagem MY-X6 SA1N-SN4 3.7V Replacement Battery 1000mAh

Sagem MY-X6 / MY-X7 Series — 3.7V Li-ion Replacement Battery (SA1N-SN4)

This is a 3.7V, 1000mAh Li-ion cell replacing OEM part SA1N-SN4 in Sagem candybar-style phones from the mid-2000s. It fits the MY-X6, MY-X7, MYV-65, MYV-75, and several additional models sharing the same battery bay and connector. Voltage and capacity match the original spec exactly.

• MY-X6 / MY-X7 platform fit: These models share a common battery bay geometry, connector pitch, and charge IC voltage range. The same cell works across the cluster because Sagem held the 3.7V nominal rail and physical form factor constant across that generation.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the MY-X6 platform. The BMS accepted the cell without fault codes, charge termination fired correctly at 4.2V, and the protection circuit tripped cleanly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The MY-X6 fuel gauge IC was calibrated to the original cell's discharge curve — one full cycle resets that baseline against the new cell.

Sudden shutdown at 20–30% on the MY-X6 after a cell swap

The MY-X6's fuel gauge IC holds a discharge model built from the previous cell's internal resistance and voltage curve. A fresh cell has lower internal resistance and a different voltage-versus-capacity slope. When the phone predicts 20–30% remaining using the old model, the new cell may actually be near its voltage cliff. Under GSM modem transmit bursts — which pull sharp current spikes — terminal voltage drops below the shutdown threshold instantly. The fix is one full discharge-charge cycle so the coulomb counter resets its end-point register against the new cell's actual behaviour.

Phone won't power on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If this battery has been sitting, its open-circuit voltage may have dropped below 3.0V — the threshold where the MY-X6's BMS enters lockout to prevent cell damage. The phone will show no response to the power button or charging. Connect the original Sagem charger and leave it for 20–30 minutes without touching the phone; the charge IC trickle-charges the cell at a low current rate until voltage recovers above 3.0V, at which point the BMS re-enables and normal charging resumes. If the screen stays dark past 45 minutes on charge, check that the charger output is confirmed at 5V.