2x Pack - Replacement Sennheiser RS 4200 Battery - For Sennheiser BA300, Set 830-TV, RI 830, Set 830 S, RI 830 S, IS 410, RI 410, RR 4200 Headphone Battery (150mAh, 3.7V, Lithium Polymer) Replacement Sennheiser RS 4200 Battery Replacement for Sennheiser BA300 Headphone Batteries Quantity: 2, Lifetime Warranty Capacity: 150mAh, Upstart Battery Brand On Sale for a Limited Time!