About this replacement
Logitech S715i / S315i — 3.6V Ni-MH Replacement Battery (180AAHC3TMX)
This 3.6V, 1500mAh Ni-MH battery replaces the original rechargeable cell in the Logitech S715i and S315i portable speakers. It fits the internal battery compartment directly and restores power to speakers where the original pack no longer holds a usable charge. Capacity figure is 1500mAh (5.4Wh) as specified in the product data.
- S715i and S315i platform fit: Both models share the same 3.6V Ni-MH cell format, connector pitch, and internal BMS handshake requirements — which is why one battery covers both. The cell dimensions (49.66 × 28.70 × 26.78mm) match the original housing cavity without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the S715i platform and confirmed the BMS accepted the pack without fault codes, held charge across multiple cycles, and delivered stable voltage through the amplifier and Bluetooth radio simultaneously.
- Ni-MH discharge discipline for the S715i: Ni-MH cells in always-docked speakers develop voltage depression when repeatedly topped off from 70–80% without a full cycle. Run the S715i down below 20% at least once a month before recharging — this keeps cell voltage balanced and prevents premature capacity loss specific to Ni-MH chemistry.
Audio distortion before the battery indicator reaches empty on the S715i
The S715i amplifier draws a current spike at higher volume levels. When the Ni-MH cell is aged or partially sulfated, internal resistance rises and voltage sags under that spike — even if the fuel gauge still reads 30–40%. The amplifier clips before the battery indicator hits zero because the cell can no longer sustain the instantaneous current demand. Replacing the cell restores the voltage floor; confirm the pack is holding above 3.4V under load after a full charge.
Speaker shows full charge immediately after plugging in — then dies within minutes
This is a classic Ni-MH memory effect symptom on a cell that has been shallow-cycled for months. The battery reads full because the charger circuit sees voltage recover quickly, but actual usable capacity has collapsed. The BMS is not faulty — the cell itself can no longer sustain discharge. Fitting a fresh 1500mAh cell and running two full discharge-recharge cycles will reset the baseline and restore normal behaviour.