Sony MDR-RF860 MDR-RF4000 MDR-RF970 MDR-RF970RK MDR-RF925 700mAh Replacement Battery This is a replacement Sony Headphone Battery Capacity: 700mAh (0.7Ah) Chemistry: Ni-MH SONY MDR-RF4000, MDR-RF4000K, MDR-RF810, MDR-RF810RK, MDR-RF840, MDR-RF840RK, MDR-RF850, MDR-RF850RK, MDR-RF860, MDR-RF860RK, MDR-RF925, MDR-RF925RK, MDR-RF970, MDR-RF970RK Replacement Batteries Mfgr Part # Sony BP-HP550-11