Recharging Magical Items (DMG)

Some items that carry several charges are rechargeable. Recharging isn't easy, but it is easier than creating an entirely new magical item. High-level wizards or priests may find it useful to boost up an old item.
To recharge an item, it must first be enchanted either through the use of an enchant an item spell or prayer, as noted above. Once prepared, new charges can be cast into the item. One benefit of recharging an item is that each charge requires only the spells' normal casting time (not the 2d4 hours per spell level normally required by the enchant an item spell).
However, recharging is not without risk to the item. Each time the item is enchanted to recharge, it must roll a saving throw vs. spell (using the saving throw of the caster) with a -1 penalty. If this saving throw is failed, the character has accidentally interfered with the magic of the item and it crumbles into useless dust.