About this replacement
AudioVox CDM-8600 / CDM-8500 — 3.7V Li-ion Replacement Battery (BTR-8500)
This is a 3.7V, 1000mAh Li-ion cell built to the BTR-8500 spec. It fits the AudioVox CDM-8600 and CDM-8500 handsets. Swap it in when the original cell no longer holds charge through a normal day of calls and messaging.
- CDM-8600 and CDM-8500 compatibility: Both handsets run the same 3.7V rail and use the same BTR-8500 connector footprint. The BMS handshake is identical across both models, so one cell covers the full platform without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the CDM-8600 chassis. The BMS engaged charge termination correctly at 4.2V and held cut-off at the low-voltage threshold without tripping prematurely under call-load current draw.
- Fuel gauge recalibration after install: On the CDM-8600, the fuel gauge IC retains the discharge curve of the old cell. After fitting this battery, run one complete discharge to auto-off, then charge to 100% without interruption. This lets the IC map the new cell's actual curve before it starts reporting percentage to the OS.
Why the CDM-8600 shuts off suddenly at 20–30% battery remaining
This is a voltage cliff, not a capacity problem. When an aged cell can no longer sustain voltage under the current spike of a GSM transmission burst, the phone's protection circuit cuts power before the OS registers low battery. A fresh 1000mAh cell with lower internal resistance handles the surge load without the voltage drop that triggers the cutoff. After installing this battery, run a full discharge-to-charge cycle so the fuel gauge IC recalibrates its low-voltage threshold to the new cell's actual discharge curve.
Phone reads 100% immediately after install, then drops fast in the first hour
The CDM-8600 fuel gauge IC stores a coulomb count calibrated to the old, degraded cell. It has no way to know the new cell's true capacity until it runs a full cycle. The percentage will look accurate after the first complete discharge and uninterrupted recharge. Do not judge the replacement cell's capacity from the first two partial cycles — let it finish a full cycle from auto-off shutdown to 4.2V charge termination first.