Motorola V66 Replacement Battery SNN5611A 3.7V 750mAh

Motorola V66 / V66i / V66c — 3.7V Li-ion Replacement Battery (SNN5611A)

This is a 3.7V, 750mAh Li-ion battery for the Motorola V66, V66i, and V66c mobile phones. It replaces OEM part numbers SNN5611A and SNN5609B. If your original cell has degraded and the phone no longer holds a charge through a normal day, this swap restores full capacity.

• V66, V66i, and V66c compatibility: All three models share the same battery bay dimensions, connector pinout, and 3.7V voltage rail. One cell fits all three without modification.
• Bench tested on actual hardware: We cycled this cell through a full discharge and charge sequence on the V66 platform. The BMS accepted the charge handshake cleanly and hit the rated 750mAh within the first two cycles.
• Fuel gauge recalibration on first use: On first installation, disable any fast-charge accessory and run one complete discharge-to-charge cycle. The V66's fuel gauge IC calibrates against the cell's discharge curve on that first pass — skipping it causes the percentage readout to drift until the IC catches up.

Why the V66 shuts down suddenly at 20–30% after a cell swap

The V66's fuel gauge IC holds a discharge curve learned from the original cell. A new cell has a different internal resistance profile, so the IC misjudges how much voltage the cell will drop under the load of an active call or backlight burst. When the cell voltage dips below roughly 3.2V under that transient load, the BMS trips a hard cutoff — even though the reported percentage still looks healthy. Running one full discharge cycle lets the IC relearn the curve against the new cell and stops premature cutoff.

Phone shows 100% immediately after installation and drops fast

This is the fuel gauge IC reporting against a stale coulomb count, not the actual cell state. The IC does not auto-reset on cell swap — it carries over the last known charge state from the old cell. The fix is straightforward: drain the phone to auto-shutoff, then charge uninterrupted to full. After that single cycle the IC resets its reference point to the new cell's actual capacity, and percentage readings stabilise.