Charged items are an interesting sort of PC find. Because they have a cost, there’s generally some real benefit to using them, but because there’s a cost there’s also some motivation not to use them for every little thing. Also, because charges are generally non-renewable even unbalancing items tend to go away eventually. And they’re usually a lot more interesting than “+3 to some roll or other”. This all seems like a win except for one small detail: keeping track of charges is a pain.

It’s a pain because it’s easy to forget to do it, and because there’s a question of who should be tracking (players? do they know the exact number of charges?). It’s also a pain because different numbers of charges remaining can cause real changes in the way players use the items: a wand with 50 charges left feels almost inexhaustible; one with 3 charges left may be hoarded, even at the cost of PCs’ lives. To some degree this reflects the should-I-use-this-or-not interesting choice mentioned above, but it generally fails to emulate the way a character would act when feeling threatened, the tendency to keep pulling the trigger until ammo runs out. And of course it’s impossible for the PC to run out of ammo without the player knowing it’s about to happen, unless the DM is the one actually tracking charges remaining (as if the DM needs more numbers to juggle!)

Solve this by not tracking a definite number of charges, but by assigning each item a percentage that the next use will be its last. The percentage can be calculated by dividing 100% by the number of charges you’d normally assign the item, so for a wand with 50 charges that’s 100%/50 = 2%; for a staff with 8 charges it’s 100%/8 = 12% (actually 12.5, but let’s round down). There are of course a few items that should still have charges tracked explicitly, generally those in which charges are iconic and small in number (e.g. a Ring of Three Wishes).

The way this looks in play would be that a player would have their character use the item, then roll against this depletion chance; as long as they roll over the percentage the item remains usable (note that the percentage doesn’t change as the item is used); otherwise the item is used up. You can probably just tell players the depletion percentage for an item (or wait until they use something like Identify to get a sense of how charged it is), since this number doesn’t provide any definitive information on how many times it can be used – an item with a 4% depletion chance may fail after the first use, and one with a 25% depletion chance may be useful after a dozen invocations.

In short, this change reduces the amount of tracking that has to be done during the game, increases unpredictability, and tries to make players more likely to use items as charges dwindle rather than bypass them on character sheets until they’re forgotten.