Whether you need to replace a lost charging unit or simply desire simultaneous charging of your front and rear derailleur batteries, the SRAM Battery Charger has you covered with its simple operation, LED charging status, and convenient power options. It works with any USB power source and USB wall adapters, taking only 60 minutes to complete a full charge. And even though each eTap battery lasts an incredible 1000 kilometers (that's 600 miles!), it's certainly nice to have a second Battery Charger on hand when you need to juice up your derailleur batteries in a pinch.