Mегафон SP-W1 Replacement Battery 3.7V 1100mAh Li-ion

Mегафон SP-W1 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1100mAh Li-ion replacement battery for the Mегафон SP-W1 smartphone. It slots into the SP-W1 battery bay and restores power to a phone that no longer holds a charge. Rated at 4.07Wh, it matches the original cell's voltage and form factor at 84 × 34 × 4mm.

• SP-W1 fit: The SP-W1 uses a removable slim-pack cell at 3.7V nominal. This replacement matches that voltage rail and physical footprint, so the battery seats correctly and the charge IC sees the expected cell parameters on first boot.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the bench. The BMS engaged charge cutoff cleanly at 4.2V and held low-voltage protection without tripping prematurely under steady load.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before the charge IC pushes higher current into an uncalibrated cell.

Sudden shutdown at 20–30% on the SP-W1 after a cell swap

This happens because the fuel gauge IC is still using the discharge curve it learned from the old, degraded cell. When the new cell hits a steeper voltage drop under screen or modem load, the IC hasn't mapped that curve yet and calls an early shutdown. It reads 25% but the voltage has already dropped below what the protection circuit allows under load. Running one complete discharge cycle — draining to automatic shutoff, then charging uninterrupted to 100% — forces the coulomb counter to rebuild its reference against the new cell.

SP-W1 not powering on after the replacement battery sat in storage

Li-ion cells self-discharge in storage, and if the cell drops below roughly 2.5V the BMS trips into lockout to prevent damage. A phone that won't respond to the power button after weeks on a shelf is almost always in BMS lockout, not a dead cell. Connect the SP-W1 to a charger and leave it untouched for 15–20 minutes — the charge IC will trickle current into the cell until voltage climbs above the BMS recovery threshold. Once voltage crosses approximately 3.0V, the BMS re-initialises and the phone boots normally.