Sagem 920 Replacement Battery 3.7V 900mAh Li-ion

Sagem MC920 / 930 / 940 / 950 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 900mAh Li-ion battery for the Sagem MC920, MC930, MC940, and MC950 mobile handsets. These are compact early-2000s phones that share the same battery bay dimensions and connector orientation across the range. Capacity figure is 900mAh — that is the rated cell spec for this listing.

• MC920–MC950 compatibility: The 920, 930, 940, and 950 share the same battery form factor, contact pitch, and 3.7V single-cell architecture. No hardware modification is needed to fit any model in this range — the connector seats the same way on each.
• Bench tested on actual hardware: We cycled this cell through a full charge-discharge sequence and confirmed the BMS held charge termination at 4.2V per cell. Discharge cutoff triggered cleanly without premature BMS trip under normal load conditions.
• Fuel gauge recalibration on first use: After fitting the new cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The MC920's fuel gauge IC was calibrated to the original cell's discharge curve — one full cycle resets that baseline against the new cell so percentage readings stay accurate.

Why the MC920 shuts off suddenly at 20–30% after a cell swap

The MC920 uses a simple coulomb-counting fuel gauge that tracks charge state against a stored discharge curve from the original cell. A new cell has a different internal resistance profile, so the gauge misreads remaining capacity. When the phone demands a brief current spike — during a call setup or screen wake — the new cell's voltage drops below the shutdown threshold even though the gauge still shows charge remaining. One complete discharge-charge cycle writes a new baseline into the gauge and closes the gap between reported and actual charge state.

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

Li-ion cells self-discharge in storage, and the MC920's BMS locks out the cell if voltage drops below approximately 2.5V — a protection against accelerated degradation from deep discharge. The phone will show no response at all: no boot screen, no charging indicator. Connect the phone to a low-current charger such as a USB wall adapter at 500mA or less and leave it for 20–30 minutes before attempting to power on. This allows the BMS to detect trickle current, release the lockout, and bring cell voltage back into the normal operating window above 3.0V before a full charge cycle begins.