ACE Caracas N4L120J Replacement Battery 3.7V 1700mAh

ACE Caracas / Caracas 2 — 3.7V Li-ion Replacement Battery (N4L120J)

This is a 3.7V, 1700mAh Li-ion cell built to fit the ACE Caracas and Caracas 2 smartphones. It replaces OEM part number N4L120J directly. If your original battery no longer holds charge or the phone shuts down unexpectedly, this cell restores full operation.

• Caracas and Caracas 2 compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS communication protocol — that is why one cell covers both. The 66.20 × 44.00 × 5.10mm footprint fits the housing without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Caracas platform. The BMS handshake completed correctly, charge current stepped down at the expected voltage threshold, and the protection circuit tripped cleanly on a simulated over-discharge condition.
• 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 for the new cell before high-current charging pushes current into an uncalibrated state — otherwise percentage readings will drift.

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

A new cell has a steeper voltage-drop curve than the aged cell the fuel gauge IC was trained on. When modem activity or screen brightness spikes current draw, the cell voltage dips sharply — the phone interprets this as a critical low-voltage event and shuts down, even though the displayed percentage still reads above zero. One full discharge-to-zero and charge-to-100% cycle lets the coulomb counter re-anchor its curve to the new cell. After that cycle, the shutdowns stop.

ACE Caracas not powering on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If the N4L120J cell sat uninstalled for several months, its resting voltage may have dropped below 2.5V — the threshold at which the BMS locks out to prevent cell damage. The phone will not respond to the power button in this state. Connect the phone to a wall charger and leave it for 15–20 minutes without pressing anything; the charge IC will trickle current into the cell until the BMS unlocks, at which point normal charging resumes. If the charge indicator does not appear after 30 minutes, check that the charger is delivering at least 5V 1A.