Reading a scroll of charging allows you to select an object in your inventory to charge, or (if read while confused) to increase your energy to the maximum. If you already were on maximum power you will gain 5d4 maximum energy.
You can recharge all wands and tools that have charges. You can also charge rings that have numeric enchantments (such as adornment), in order to increase their enchantment. There is a risk that rings (or wands that have previously been recharged) will explode. Wands of wishing and magic markers cannot be recharged more than once.
Because of the scroll's function, two blessed scrolls of charging are often the best first wish to make from a wand of wishing, to use when its initial charges run out. A blessed scroll of charging will typically restore more charges than an uncursed scroll.
A cursed scroll of charging will not restore any charges, although it will still increment the charge counter, set the current number of charges to zero (or decrease a ring's enchantment by 1-2), and possibly cause wands and rings to explode.