About this replacement
Altec Lansing IM600 / IMT620 Series — 3.7V Li-ion Replacement Battery (MCR18650)
This is a 3.7V, 2200mAh Li-ion cell replacing the MCR18650 in the Altec Lansing IM600, IMT620, IMT702, and iMT520 portable speakers. It restores wireless playback when the original cell has degraded or failed. Voltage and capacity match the OEM spec exactly.
- IM600 / IMT620 / IMT702 / iMT520 compatibility: These models share the same internal cell bay, connector orientation, and BMS communication protocol — all run a single 18650 cell on a 3.7V rail with identical charge acceptance circuitry, so one cell fits all four platforms.
- Bench tested on actual hardware: We ran the MCR18650 through full charge and discharge cycles on the IM600 board. The BMS accepted the cell without fault codes, and the protection circuit tripped correctly at low-voltage cutoff with no thermal anomalies under sustained audio load.
- Monthly discharge cycle for the IM600 series: These speakers are commonly left on a desk and topped off constantly. Let the cell drop below 20% at least once a month before recharging — continuous shallow cycling without a full discharge causes fuel gauge drift and accelerates capacity fade on the 18650 cell.
Audio distorting before the battery indicator hits empty on the IM600
As the 18650 cell discharges toward its lower voltage threshold, internal resistance rises. The amplifier draws a current spike during loud passages that the weakening cell can't sustain cleanly, causing voltage sag at the amp rail. The speaker's audio circuit clips under that sag before the battery indicator registers critical. A fresh cell with lower internal resistance eliminates the sag and pushes clipping well past the low-battery warning.
Speaker won't wake from USB charge after sitting unused for weeks
A deeply discharged 18650 cell can drop below the minimum acceptance voltage that the USB charge controller requires to begin a charge cycle — typically around 2.5V. The charger sees an unresponsive cell and refuses to engage. Most IM600-series boards include a pre-charge trickle mode, but if the cell has dropped below roughly 2.0V the BMS will block even that. Connecting to a USB port and leaving it for 30–60 minutes without touching the power button gives the trickle circuit time to bring the cell back above the acceptance threshold before a normal charge can begin.