Seecode S40 Nokia N6 Replacement Battery 3.7V 750mAh

Seecode S40 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 750mAh Li-ion cell for the Nokia N6 running the S40 platform. It slots into the original battery bay and connects to the same charge management circuit the phone shipped with. Capacity matches the original spec at 2.78Wh.

• S40 platform fit: Nokia's S40 devices share a standardised battery bay geometry and charge IC interface. This cell matches the contact layout and voltage curve the N6's charge management IC expects — no adapter, no rewiring.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an N6 unit. The BMS accepted charge current from the first connection, and the phone's charge IC held a stable taper current to termination without triggering an early cutoff.
• Fuel gauge recalibration on first use: After fitting this cell, run one full discharge to phone-off, then charge uninterrupted to 100% before normal use. The N6's fuel gauge IC was calibrated to the old cell's discharge curve — skipping this step causes the percentage readout to track incorrectly from the start.

Sudden shutdown at 20–30% on the N6 after a cell swap

The N6's fuel gauge IC stores a discharge model from the old cell. When a new cell is fitted, the IC's shutdown threshold fires based on stale voltage-to-capacity mapping, not the actual remaining charge in the new cell. Under modem or screen load, voltage sags briefly below the stored cutoff point, and the phone shuts down even though the cell has usable capacity left. One full discharge-charge cycle rewrites the IC's reference points against the new cell's actual voltage curve, and the early shutdowns stop.

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

Li-ion cells self-discharge during storage. If this cell sat long enough to drop below 2.5V per cell, the BMS has tripped into lockout to prevent damage to the chemistry. The phone will show nothing when you press the power button — not a low-battery screen, nothing. Connect the phone to a wall charger and leave it for 15–20 minutes without pressing anything; the charge IC will trickle current into the cell until it clears the BMS threshold and the device recovers. If the screen still shows nothing after 30 minutes on charge, check the charger output is reaching 5V at the connector.