About this replacement
Altec Lansing Omni Jacket / iMW678 — 3.7V Li-ion Replacement Battery (INR18650-3S1P)
This is a 3.7V, 7800mAh Li-ion replacement battery for the Altec Lansing Omni Jacket portable Bluetooth speaker, covering model numbers iMW678, iMW678-BLK, iMW678-BLU, and five additional variants. It slots into the same position as the original INR18650-3S1P pack. Capacity is rated at 28.86Wh, matching the original cell configuration.
- iMW678 series compatibility: All listed iMW678 variants share the same 3S1P 18650 cell configuration, connector pinout, and BMS handshake requirements. The fuel gauge IC in the speaker reads cell voltage directly, so the replacement pack must match the 3-cell series arrangement — this one does.
- Bench tested on actual hardware: We cycled this pack through charge and discharge on the iMW678 platform and confirmed the BMS handshake completed without error flags. The protection circuit triggered correctly at low-cell cutoff, and the charger accepted the pack without cycling into fault mode.
- Fuel gauge reset after install: The iMW678's onboard fuel gauge can carry over stale state-of-charge data from the old pack. After fitting the new battery, run it down to the single LED warning indicator before the first full recharge — this lets the gauge recalibrate to the new cell's actual capacity curve.
Capacity fade from constant desk-top charging on the iMW678
The Omni Jacket is frequently used as a desk speaker and kept plugged in continuously. Li-ion cells held at 100% state of charge and elevated temperature — common when the amplifier and charger run simultaneously — degrade faster than cells that cycle through a full discharge. The BMS in the INR18650-3S1P pack limits overcharge, but it cannot prevent the long-term stress of float charging at full voltage. To slow capacity loss on a replacement pack, unplug the speaker once charged and let it discharge below 20% at least once a month before recharging.
Audio distorting before the battery indicator reaches empty
As cell voltage drops under load, the amplifier inside the iMW678 receives less headroom and begins clipping audio waveforms before the fuel gauge reads zero. This sounds like crackling or harshness at moderate-to-high volume, even with apparent charge remaining. The cause is voltage sag under the combined draw of the amplifier and Bluetooth radio — not a speaker driver fault. If distortion appears with charge still showing, charge the battery to full and check whether the symptom moves; if it disappears above 3.9V per cell, the pack is approaching end-of-life.