Mегафон 602 Replacement Battery 3.7V 800mAh Li-ion

Mегафон 602 — 3.7V Li-ion Replacement Battery

This is a 3.7V 800mAh (2.96Wh) Li-ion replacement battery for the Mегафон 602 basic mobile phone. It fits directly into the 602 and restores power to devices where the original cell has degraded or failed to hold charge. Dimensions are 49.34 × 40.00 × 4.45mm — verify against your existing battery before installing.

• Mегафон 602 fit: The 602 runs a single-cell 3.7V Li-ion configuration with a low-current BMS suited to a basic phone draw profile. This cell matches that voltage rail and physical footprint.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted charge without tripping, and the protection circuit cut correctly at the low-voltage threshold without locking the cell into a fault state.
• Fuel gauge recalibration on first use: After installing a new cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The 602's fuel gauge IC reads the old cell's discharge curve by default — one complete cycle overwrites that reference and corrects percentage reporting.

Sudden shutdown at 20–30% on a replacement cell in the Mегафон 602

This happens because the fuel gauge IC is still calibrated to the old cell's discharge curve. When the new cell hits a voltage point the IC wasn't expecting, the phone interprets it as a critical low-voltage event and cuts power — even though the displayed percentage looks safe. The fix is a single full discharge-to-shutdown followed by an uninterrupted full charge. After that cycle, the IC recalibrates its coulomb counter against the new cell and the shutdowns stop.

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

Li-ion cells in storage self-discharge slowly. If this battery dropped below approximately 2.5V per cell before installation, the BMS protection circuit may have triggered a lockout to prevent damage from deep discharge. Connect the phone to a charger and leave it for 15–20 minutes without attempting to power it on — the charge IC needs to push a small trickle current through the locked-out BMS to bring cell voltage back above the recovery threshold. Once voltage recovers past that floor, the BMS releases and normal charging resumes.