Sony MDR-RF860 Wireless Headset Compatible Battery 2.4V 700mAh

Sony MDR-RF860 / MDR-RF970 Series — 2.4V Ni-MH Replacement Battery (BP-HP550-11)

This is a 2.4V, 700mAh Ni-MH replacement battery for the Sony MDR-RF860, MDR-RF970, MDR-RF970RK, MDR-RF4000, and compatible wireless headsets. It replaces OEM part BP-HP550-11 and fits directly into the headset's battery compartment. When the original cell degrades and the headset stops holding a charge, this swap restores full wireless operation.

• MDR-RF860 and RF970 series compatibility: These models share the same 2.4V two-cell Ni-MH pack format, battery bay dimensions, and connector pinout. The base station charges the pack through the same contact rails across all compatible variants, so one part number covers the full range.
• Bench tested on actual hardware: We ran this pack through the MDR-RF860 base station charge cycle. The BMS accepted the new cell without error flags, completed a full charge cycle, and the headset paired cleanly to the transmitter at 2.4V nominal output.
• First-cycle base station protocol: Place the headset in the base station and complete one full uninterrupted charge before using it. Sony's receiver firmware logs the new cell's state during this cycle — skipping it causes the talk-time indicator to read inaccurately until the base resets its capacity reference.

Why the MDR-RF860 cuts out mid-transmission on a new battery

The RF860 draws current simultaneously from the audio amplifier and the 2.4GHz DECT radio module. During active transmission, that combined draw spikes briefly above the resting load. A new Ni-MH cell at storage voltage — typically around 2.2V — hasn't yet stabilised at its rated 2.4V operating point. The BMS reads the momentary sag as a low-cell event and cuts the headset to protect the pack. Two or three full charge-discharge cycles bring the cell to rated voltage and eliminate the dropout.

Base station showing a charging error after fitting the new pack

Sony base stations use a delta-peak detection method to confirm charge completion. If the new cell arrives at a very low state of charge, the base may not detect the initial voltage rise it expects and flags a fault instead of starting the cycle. Remove the headset, leave it out for 30 seconds, then reseat it firmly so all three charge contacts are flush. If the error persists, check that the cell voltage at the contacts reads at least 2.0V with a multimeter — anything below that requires a slow pre-charge before the base will accept it.