Sennheiser 0121147748. 100% compatible for Sennheiser batteries - Fully compatible with Sennheiser MM 400, 450 X, 400 X, 550, 450, 500 X, PX 210 BT, 360, 360 BT, 310 BT, PXC 310, 310 BT, 360 BT, 450 TRAVEL, 550 Travel, MM-550 X, PCX 360 BT.
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