Sennheiser SK9000 Replacement Battery 3.7V 1800mAh Li-ion

Sennheiser SK9000 Bodypack Transmitter — 3.7V Li-ion Replacement Battery (56429 701 098)

This 3.7V, 1800mAh Li-ion cell replaces the internal battery in the Sennheiser SK9000 bodypack transmitter. The SK9000 is a professional wireless microphone transmitter used in live performance, broadcast, and presentation environments. Also cross-references OEM part numbers 504703, B61, and BA 61.

• SK9000 bodypack compatibility: The SK9000 transmitter runs a combined audio processing and RF transmission load from a single cell. This replacement matches the original cell's voltage rail and physical footprint, so the BMS handshake with the transmitter's internal management circuit completes correctly on first charge.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles under combined audio and RF draw. The BMS held stable cutoff thresholds and the transmitter's charge indicator tracked accurately from the first full cycle.
• First-charge protocol for the SK9000: After fitting the new cell, allow the transmitter to complete one full charge cycle before use in a live setting. The SK9000's onboard fuel gauge calibrates against the new cell's capacity profile during that first cycle — skipping it causes the charge indicator to under-read for several sessions.

Why the SK9000 transmitter runs warm during extended live sets

The SK9000 packs audio capture and RF transmission into a compact bodypack housing with minimal thermal mass. Sustained combined draw from both circuits raises cell temperature more than either load alone would. This is normal within the transmitter's operating envelope, but heat shortens cell life over time if the unit is stored hot after use. Let the transmitter cool to ambient before slotting it into a case or charging cradle after a long set.

SK9000 shows a full charge but the transmitter cuts off early in use

This is a storage voltage issue. A new cell arrives at a partial storage charge — typically around 3.6V — and the transmitter's fuel gauge reads that as near-full before the BMS has logged a complete cycle. The cutoff happens because the cell hits its low-voltage threshold sooner than the indicator predicted. Run one full charge-to-discharge cycle and the gauge recalibrates; subsequent charge readings will track accurately against the 1800mAh capacity.