Vertu Constellation Ayxta BL-4UV Replacement Battery 3.7V 1200mAh

Vertu Constellation Ayxta — 3.7V Li-ion Replacement Battery (BL-4UV)

This is a 3.7V, 1200mAh Li-ion cell that replaces the original BL-4UV battery in the Vertu Constellation Ayxta smartphone. The Constellation Ayxta is a luxury handset with specific power requirements — a degraded cell causes erratic shutdowns and inaccurate charge readings. At 62.00 x 38.00 x 4.50mm, this cell matches the original footprint exactly.

• Constellation Ayxta fit: The BL-4UV connector pinout and physical envelope are specific to this handset. The BMS on this cell matches the voltage thresholds the phone's charge IC expects — a mismatch here prevents the device from powering on at all.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the Constellation Ayxta platform. The BMS held charge cutoff at 4.2V and triggered low-voltage lockout cleanly below 3.0V with no false trips during modem activity.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes into an uncalibrated state.

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

The Ayxta's fuel gauge IC holds a discharge curve from the original cell in memory. A new cell with a different internal resistance profile hits a voltage cliff earlier under screen or modem load than the gauge predicts. The phone sees the voltage drop as a hard shutdown condition before the displayed percentage reaches zero. One full discharge-charge cycle forces the coulomb counter to relearn the new cell's curve and eliminates this behaviour.

Phone stays warm near the battery compartment during first charges

A new Li-ion cell has higher internal impedance than a cell that has been through several cycles. The charge IC feeds the same current profile it used on the original cell, but higher impedance converts more energy to heat in the early cycles. This is normal and reduces after three to five charge cycles as the cell's impedance settles. If the device stays warm beyond five cycles, check that the charge IC is not locked in a fast-charge mode — drop to standard 5V charging and confirm the back of the phone cools within 30 seconds of plugging in.