Outside of wizard mode, wishing for a number of charges on a wand or tool gives the lesser of that number or the number it would have naturally rolled. This makes it at best a useless option (if you wish for max charges), and at worst actively harmful, so there's no reason to ever do so. I propose a way to make wishing for charges a situationally useful choice, without unbalancing the game:

• If Luck is less than zero, keep the current behavior, to be consistent with negative Luck's influence on wishes.
• Assuming non-negative Luck, if you wish for the item's average number of charges or less, you always get that many. So e.g. if you're wishing for a magic marker and want to be certain of having enough charges to write a level 6 spellbook, you can wish for 65 charges and be certain of having enough, with possible some extra to write a few scrolls.
• If you wish for more than the average charges, take the difference between the two. With 50% chance, you get the average plus the difference (i.e. the number you wished for), otherwise you get the average minus the difference. If you wish for 70 charges to write finger of death, you get either 60 or 70, with equal odds; if you get greedy and wish for 99, you get 99 or 31. So the average number of charges doesn't change, and the more charges you wish for, the fewer you risk receiving. So it adds a new wrinkle to wishing, and makes you think about how many charges you really need, or even whether you want to wish for charges at all.