Amazon.com: Sennheiser MM 550-X Wireless Bluetooth Travel Headphones : Electronics
Sennheiser MM 400-X review | What Hi-Fi?
Sennheiser MM 400-X On-Ear Wireless Bluetooth Headphones (MM400-X)
Synergy Digital Wireless Headset Battery, Works with Sennheiser MM 400-X Wireless Headset, (Li-Pol, 3.7, 270mAh), Compatible with Sennheiser 0121147748, BA 370 PX, BA370, BA-370PX Battery - Walmart.com
Nylon Audio Cable with mic For Sennheiser mm400-x mm450-x mm550-x EH2200 EH2270 | eBay