Sennheiser HD 4.50 Battery Replacement - iFixit Repair Guide
Sennheiser XSW-D Batteries - Cameras - EOSHD Forum
Amazon.com: Replacement Battery for SENNHEISER 450 Travel 550 Travel MM 400 MM 400-X MM 450 MM 450-X MM 500-X MM 550 MM-550-X PCX 360 BT PX 210 BT PX 310 BT PX