You won't regret buying an xtar I have the xtar vc4 had it well over 4 years & it's the 2 outer slots for charging the 21700.Thank you all, I'm going to buy one of the Xtar models. I originally looked at a Nitecore charger as I knew of the brand already but a lot of their chargers don't charge 21700s but they do charge larger and smaller cells. Does anyone know why this is? Its more curiosity than anything else, just seems a bit odd for their chargers to be able to charge larger cells and smaller cells but not this size.