Magic Recharging Device
As presented in Dwarves Deep the Glowstone is a gamebreaking device. The writers imagined characters using it to recharge their wands and staves with no thought to items like rings of multiple wishes and luckblades.
I wanted to keep the item in the game so I changed how it operates and made it a permanent rather than a charged item.
The description remains the same, a fist sized gem that glows as continual light and cannot be quenched by any magic darkness.
If touched to another magic item it attaches itself as if a strong magnet to iron (can be removed with a moderate effort, but cannot be accidentally bumped loose).
While attached to an item that has charges or uses per day that is not fully charged a spell caster can touch the stone and channel their mana into the stone which then converts the energy to charges or uses for the item it is attached to. The amount of mana required is equal to the highest level spell a charge can produce (a staff of power can produce a cone of cold with 1 charge so 4 mana would give 1 charge). When an item is fully charged the stone stops working (it will not overcharge and item). If too few mana points are given to charge the device the stone will hold them as long as it remains attached to the other item and more can be added later. If the stone is removed with a partial charge the remaining mana is lost. If the function of the device is a spell that would normally have a detrimental effect on the caster (such as resurrection or wish) the person charging with the glowstone must take the price as well (putting a charge into a ring of wishes would take 9 mana and age the contributor 5 years).
A Glowstone has an estimated value of 14,000 GP, but are rarely ever sold. Making one is believed to require Enchant an Item, Permanency, and Continual Light as well as exotic ingredients found deep in the underdark.