Sennheiser 450 TRAVEL 550 Travel MM 400 MM 400-X M Replacement Battery: BatteryClerk.com
Sennheiser PXC 210 BT Review: These foldable wireless headphones have perfect Bluetooth sound quality - Back to School - Headphones - PC World Australia
Sennheiser PX 210 BT review | TechRadar
Cameron Sino 270mah Battery For Sennheiser Pxc 310,mm 400,mm 450,450 Travel,550 Travel,px 210 Bt,px 360,mm 550,px 310 Bt - Digital Batteries - AliExpress
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