Every place I found so far gives 50 charges to a wand when selling it and buying it back.

There was the HighHedge shop in BG1 which gave 200 charges (I think? I never used all 200 to check.). It cost a lot, but was worth it to have a 200 charges fireball wand and 200 charges summon monster wand in Durlag's tower. :D

Is there a super nice place in BG2 (SoA part) to charge up your wands?
200 cloudkills... Oh the joy! :evil:

I think you get the same everywhere, and that the max charges is set per item, not merchant.

*sighs*
50 will have to do then.
I'll just have to conserve a bit.

One thing...

Did you know that Bag of Holding is in fact a mini shop? :evil: