NGM Tango Always 2 Replacement Battery 3.7V 900mAh

NGM Tango Always 2 / Simple — 3.7V Li-ion Replacement Battery

This 3.7V, 900mAh (3.33Wh) lithium-ion battery fits the NGM Tango Always 2 and Simple mobile phones. It replaces a degraded or failed original cell and restores full device operation — calls, messaging, and standard phone functions. Dimensions are 53.00 × 34.00 × 4.80mm, matching the original battery bay.

• Always 2 and Simple platform fit: Both models share the same battery bay dimensions, voltage rail, and connector pinout, which is why one cell covers both. The BMS handshake protocol is identical across the pair, so the charge IC accepts the replacement without errors.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a controlled bench rig. The BMS held voltage within spec across the full discharge curve and tripped correctly at the low-voltage cutoff threshold without false positives.
• Fuel gauge recalibration on first install: On first use after fitting this cell, run one complete discharge-to-charge cycle with fast charging disabled. The fuel gauge IC is calibrated to the old cell's discharge curve — one full cycle lets it reset against the new cell before high-current charging is applied to an uncalibrated state.

Why the Always 2 reports wrong battery percentage after a cell swap

The fuel gauge IC uses a stored discharge curve from the previous cell to estimate remaining capacity. A new cell has a different impedance profile, so the IC's coulomb counter starts out of sync. The phone reads the voltage correctly but maps it to the wrong percentage point on the old curve. One full discharge cycle — taken down to automatic shutdown, then charged to 100% — resets the calibration and brings the percentage display back into line.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff failure, not a capacity problem. Under screen-on or active call load, the cell voltage drops sharply near the low end of the discharge curve — faster than the fuel gauge IC predicts. When voltage hits the BMS cutoff threshold (typically around 3.0V), the phone shuts off even though the displayed percentage still shows charge remaining. The fix is to complete two full discharge-charge cycles so the IC learns the new cell's actual voltage-versus-capacity curve. After recalibration, the shutdowns stop.