Replacement Battery for SONY BP-HP550-11 Ni-MH 700mAh High Quality, high capacity, light weight rechargeable battery No memory effect. Can be charged or discharged as needed without loss of capacity. Overcharge protection, with built-in battery life microchip. Compatible Models: Sony MDR-RF860, MDR-RF4000, MDR-RF925RK, MDR-RF4000K, MDR-RF860RK, MDR-RF850, MDR-RF850RK, MDR-RF840, MDR-RF840RK, MDR-RF810, MDR-RF810RK Compatible Part #s: BP-HP550-11