The Tavern

This is a proposition for a new ability (a), than can be used if character has two or more non-empty wands of same type (eg. wand of hasting with 2 charges and wand of hasting with 3 charges).

By invoking the ability, player could combine the two wands destroying the other in process, and have the amount of charges in the destroyed wand be transferred to the preserved one (example: wand hasting with 2 charges + wand of hasting with 3 charges = wand of hasting with 5 charges).

If player has less than two non-empty wands of same type , the ability is not visible.
The ability would prompt to select the wands from inventory.
If amount of charges in charged wand would be more than maximum, player would get a warning for having charges beyond maximum being wasted.

If it feels somehow too powerful (i cannot see how), it could have some limit of evocation skill before it can be used (like 8 or 10), or a failure rate based on evo skill.

Why?
To reduce inventory clutter and needs for stashing, and possibly make evo skill more useful.

As someone who finds themselves with an enormous amount of wands with medium/low charges left in his stash, I think this would be pretty useful for reducing clutter.

The only way I could see this being too powerful is that it eliminates the decision of taking multiple of the same type of wand with you. When I play melee characters and my inventory is pretty full, I often find myself having to decide between carrying an additional offensive wand (generally of the same type I already have) just in case, or an additional type of potion.

Yes if it feels too powerful, it could have the failure chance based on evo skill mentioned on my first post.
For example: 0 skill = 90%, 5 = 30%, 10 = 10%, 15 = 3%, 20 = 1%, 25 = 0%.
Failure would result in losing of charges randomly in one wand.

Then the decision would be "do i want to carry more charges despite having a risk of losing some of the total charges available in the game".
Don't see big balance problems, as the total amount of available charges is not increased, but actually reduced statistically if you combine lots of wands (especially without high evo skill).

You would basically never do that with wands you do care about.

Why would you ever do this? This just makes you weaker, since now your wands of hasting max out at 9 charges, instead of at 18.

That doesn't matter, because you can now keep an arbitrarily large stack of extra virtual haste charges in your scroll of recharging stack inventory slot. It might be physically possible for this to be relevant for teleportation or heal wounds wands since those are at least possibly worth using nine times in a row without even one turn available to use on recharging, but then you can just dip into your scroll of teleportation or potion of heal wounds stacks.

If the three top wands were removed or changed into some other sort of items, wand-merging could even be compulsory. Autopickup could just combine the charges from a new wand into the one already in your inventory and nothing of value would be lost. Charge limits don't matter on lesser wands.

I think the overall charge limit of the wands is more likely to be relevant than the single inventory slot you save by merging them, and until we get to the point where you have to backtrack every time you want to ID anything that isn't going to change.

Possibly this would have more use with weaker wands than heal wounds in the example, at least i often skip picking up damage wand, if i already have same type in inventory.

Merging wands could grant 1d2 + (evocations/9 rounded down) charges to the wand, but not more than number of charges left on the merged wand.

Considering that the ground is your "stash" (at least in trunk), if you really need those wands you can always go back and get them. Seems like there are no real circumstances where this would be that much of a help.