NEC E606 Replacement Battery MAY-BD0007-A001 3.7V 950mAh

NEC E606 — 3.7V Li-ion Replacement Battery (MAY-BD0007-A001)

This is a 3.7V Li-ion cell rated at 950mAh (3.52Wh), built to the MAY-BD0007-A001 specification. It fits the NEC E606 smartphone directly. The cell restores power to devices where the original battery has degraded or failed completely.

• E606 platform fit: The NEC E606 uses a single-cell 3.7V Li-ion pack with a connector and BMS handshake matched to this part number. Voltage rail and cell footprint align to the original MAY-BD0007-A001 specification, so the phone's charge IC and fuel gauge IC communicate with the replacement cell without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held charge termination voltage at 4.2V and triggered low-voltage cutoff cleanly before the cell dropped below 3.0V under load. No anomalous heat during CC/CV transition.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for the first full discharge-charge cycle. This lets the fuel gauge IC build an accurate discharge curve against the new cell before high-current charging begins. Skipping this step is the primary cause of erratic percentage readings in the first week.

Why the E606 reports wrong battery percentage after a cell swap

The fuel gauge IC on the E606 stores a learned discharge curve from the old cell. When a new cell goes in, that stored curve no longer matches actual cell behaviour. The IC interprets voltage readings against the old model, so it reports percentages that drift from real capacity. One complete discharge-charge cycle — taken slowly, without fast charging — forces the IC to rebuild the curve against the new cell's actual voltage profile. After that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display triggers a load spike the cell cannot sustain at that state of charge. The cell voltage drops sharply below the phone's minimum threshold — typically around 3.4–3.5V — and the system shuts down to protect the BMS, even though the fuel gauge still shows charge remaining. It is not a fault in the cell itself; it is the fuel gauge IC firing a protection event based on a miscalibrated curve. Complete one full slow discharge-charge cycle and confirm the cell reaches a resting voltage of 4.15–4.20V at full charge before treating the shutdown as a cell defect.