The DMg has no rules for recharging magic items. Some DMs allow the use of XP and GP (if you can meet the prerequisites to make the item in the first place) to recharge items, basing the cost off the charges being recharged, e.g. putting 10 charges into a Wand of Fly would cost 1/5 the XP and GP to create a fully-charged (50 charges) wand.