Vertu Ascent BL-4V Replacement Battery 3.7V 900mAh

Vertu Ascent — 3.7V Li-ion Replacement Battery (BL-4V)

This is a 3.7V, 900mAh Li-ion replacement cell for the Vertu Ascent smartphone. It fits the BL-4V battery slot directly and restores power to the phone's processor, display, and radio stack. Capacity is 900mAh (3.33Wh) — matched to the original specification.

• Vertu Ascent BL-4V fit: The Ascent uses a specific form factor — 53.00 x 34.00 x 4.80mm — with a connector pinout that carries both power and battery ID data. This cell matches that footprint and pin layout so the phone's power management IC reads the battery correctly on boot.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the Ascent platform. The BMS accepted the cell without triggering a fault flag, and the charge IC reached termination current without cutoff errors.
• 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 build an accurate discharge curve against the new cell before high-current charging pushes current into an uncalibrated state.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff symptom. The Ascent's modem and display draw current spikes that cause a fresh cell's terminal voltage to sag below the low-voltage cutoff threshold before the fuel gauge reads empty. The fuel gauge IC is still calibrated to the old cell's internal resistance curve, so the percentage displayed doesn't reflect actual cell voltage under load. Run one full discharge down to automatic power-off, then charge uninterrupted to 100% — this resets the coulomb counter baseline against the new cell.

Phone not powering on after the battery sat in storage

Li-ion cells stored unused can self-discharge below 2.5V per cell, which triggers a BMS lockout to prevent damage. The Ascent will show no response — no boot screen, no charge indicator — when plugged in immediately after this state. Connect the phone to a low-current USB charger (500mA wall adapter, not a fast charger) and leave it for 20–30 minutes without pressing the power button. Once the BMS detects sufficient voltage recovery, typically above 2.8V, the charge IC resumes normal operation and the phone will respond.