About this replacement
Sony MDR-RF995 / WH-RF400 — 2.4V Ni-MH Replacement Battery (BP-HP800-11)
This is a 2.4V, 700mAh Ni-MH replacement battery for the Sony MDR-RF995, MDR-RF995RK, and WH-RF400 wireless headphones. It matches the OEM part number BP-HP800-11 and slots directly into the headphone battery compartment. The original cell degrades over hundreds of charge cycles — this swap restores wireless operation to the receiver unit.
- MDR-RF995, MDR-RF995RK, and WH-RF400 fitment: All three models share the same 2.4V dual-cell Ni-MH pack format and the same physical housing dimensions (46.50 × 23.30 × 11.90mm). The base station charges at a fixed current rate calibrated for this cell chemistry — swapping in a Li-ion or Li-poly pack would overcharge on every cycle.
- Bench tested on actual hardware: We cycled this cell through the Sony base station's charge circuit and confirmed the thermistor line communicates correctly. The base station terminated charge at the expected delta-V cutoff point without triggering a fault LED.
- First charge in the base station: Place the headset in the base for a full uninterrupted charge cycle before first use. The base station logs the new cell during that initial cycle — until it completes, the talk-time indicator will underreport remaining charge.
Base station not recognising the new pack after installation
The Sony RF995 base uses a delta-V detection algorithm to confirm a valid Ni-MH cell is seated. A new cell shipped at storage voltage (around 1.0V per cell) can sit below the threshold the base expects on first contact, causing the charge indicator to stay dark or flash amber. Seat the headset firmly, hold it in the cradle for 10 seconds, then remove and re-seat — this resets the contact detection. If the fault persists, confirm cell voltage with a multimeter: each cell should read above 0.9V at rest before the base will initiate a charge cycle.
Headset cuts out mid-transmission on a freshly charged pack
The RF995 draws current from two sources simultaneously — the audio amplifier and the 2.4GHz RF receiver. On a cell that is new or has been sitting at storage voltage, that combined load briefly pulls terminal voltage below the headphone's low-voltage cutoff, which trips the protection circuit and kills audio. This is not a faulty cell — it is a conditioning issue. Run three full charge-and-discharge cycles through the base station and the dropout threshold will stabilise. After three cycles, resting voltage between charges should hold above 2.2V under no-load conditions.