AudioVox BTR-4000 Replacement Battery 3.7V 1050mAh

AudioVox CDM-4000 / CDM-4500 / CDM-9000 — 3.7V Li-ion Replacement Battery (BTR-4000)

This is a 3.7V Li-ion replacement battery rated at 1050mAh (3.89Wh) for the AudioVox CDM-4000, CDM-4500, and CDM-9000 mobile phones. It replaces OEM part number BTR-4000 and fits the original battery bay without modification. When the factory cell no longer holds a charge, this swap restores basic phone function.

• CDM-4000 / CDM-4500 / CDM-9000 compatibility: All three models share the same BTR-4000 form factor, connector pinout, and 3.7V nominal voltage rail. The BMS handshake on each device recognises this cell without firmware conflict.
• Bench tested on actual hardware: We cycled this battery through charge and discharge on the CDM platform. The BMS accepted the cell on first insertion, charge current ramped correctly through CC/CV stages, and no overcurrent trips were logged.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging if available and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before reporting an accurate state-of-charge reading to the OS.

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

This is a voltage cliff problem, not a capacity problem. Under peak modem transmit load or backlight demand, a fresh cell that hasn't been calibrated can sag below the BMS cutoff threshold even when the fuel gauge still reads 25%. The phone's protection circuit cuts power to prevent cell damage. One full discharge-charge cycle lets the coulomb counter anchor its low-voltage endpoint to the actual cell, pushing the cutoff point to a realistic level. After calibration, shutdowns below 20% should stop.

Phone won't power on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If a replacement cell drops below roughly 2.5V, the BMS enters lockout mode and blocks all charge current to prevent a hazardous charge into a deeply depleted cell. The phone shows nothing — no charging indicator, no boot. Connect the device to a wall charger, not a PC USB port, and leave it undisturbed for 20–30 minutes. A wall charger delivers enough current to trigger the BMS trickle-charge recovery routine; once the cell climbs above 2.9V, normal charging resumes and the phone will power on.