2x Pack - Sennheiser RR 4200 Battery - Replacement for Sennheiser BA300 Headphone Battery (150mAh, 3.7V, Lithium Polymer) Replacement Sennheiser RR 4200 Battery Replacement for Sennheiser BA300 Headphone Batteries Quantity: 2, Lifetime Warranty Capacity: 150mAh, Upstart Battery Brand On Sale for a Limited Time!