All you have to do is make one feat.
Reacharge Power (Item Creation)
Prerequisites: Craft Staff, Craft Wand
To Recharge an item it must have charges to begin with. Even some items that have charges may not be recharged. This feat allows you to recharge Wands and Staff's. It takes 1 day to recharge a wand for every 100gp in its base charge price and 1 day per 50 gp in the base charge price to recharge a staff.
Special: You may only recharge items you have created yourself.
To detirmine the base charge price of recharging an item you simply take the base cost of the item and divide this by the total number of charges+10 to get the gp value per charge, and divide by another 25 to get the xp cost. That gives you the price per charge now simply decide how many charges you would like to put back into the item. then multiply the base charge cost by the number of charges you want. You must also cast the spell you want to recharge into the wand once per day of crafting. You may not increase a wand or staffs number of charges to above the maximum set at its creation.
For example lets take a wand of fireball at a 10th level caster. Base price normally 11,250 gp 450 xp. Now lets say you wanted to put another 13 charges back into this after some adventuring since you have plenty of downtime but not enough gold to create a whole new one. So simply divide the normal base price by max charges+10.
11,250 / 60 = 187 gp (rounded down)
Now divide this number by 25 to get the xp price per charge.
187 / 25 = 7 xp per charge (once again rounded down for simplicity)
So each charge costs 187 gp and 7 xp and you want 13 charges.
187 x 13 = 2,431 + 7 x 13 = 91
So to recharge your wand of fireball you would need to spend 2,431 gp. on variouse alchemical mixes and other focuses to impart your magic back onto the item. And 91 xp also imparting bits of yourself onto it again. All of this would take you 24 days nearly a month of adventuring time.
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My main ideas for above would be that it could cost a little less on the monetary side of things while costing them ALOT more on the time scale. Along with having to cast the spell everyday so you couldnt very well do it very easily while adventuring. The increased time also has to do with an idea of mine that it would take alot more time to impart magical abilitys on materials that are 'stale' compared to making a fresh spankin new wand.
Alternativly you could turn the recharge wand and staff into two seperate feats to make it even a lil bit harder.
What do you all think?