The scroll of charging is an immensely useful magical item in the Nethack and Slash'em games. Its most common use is to recharge items that have a finite number of charges (wands, magic markers, spellbooks and the like), and is especially useful in conjunction with a wand of wishing. Indeed, wishing for a scroll of charging is an effective way to wish for more wishes. All rechargeable items have a finite number of times they can be recharged, after that they either disintegrate, or worse, explode in your face. The latter possibility means that recharging your wand of death one time too many is not at all a good thing.
A less well-known effect of the scroll of charging is what happens if it is used on certain rings. If used on a ring of increase accuracy, ring of increase damage, ring of protection, ring of adornment or either of the other rings that improve attributes, an uncursed or blessed scroll of charging will improve the ring's bonus by +1 (a cursed one subtracts one from the bonus instead).
If a character affected by confusion recites a scroll of charging, he will charge himself! If the character's Power is at maximum, the character will gain 5-20 maximum Power, otherwise his Power is increased to maximum.
In some versions of the game, a scroll of charging can recharge a magic lamp, trapping yet another djinni inside it for another shot at getting a wish.