This very hard spell is a way to by pass the 6ft limit on powerstone recharging. Despite the name the item isn't actually a rack per say but rather a complex network of wire made from several precious metals in which the powerstones sit.
The item requires the Jeweler skill (-7 if someone but the enchanter makes it; -5 otherwise) and on it own can only take 1 point of damage. Also other then the old version of Charge Powerstone no other enchantments can be placed on the item. For this reason traveling versions are in at least a wooden box of DR 4.
If either the Jeweler roll or Enchantment roll fail the enchanter must start from the beginning.
Since the spell also requires $75,000 worth of materials and has an asking price of $25,000 per stone no Powerstone Recharging Rack containing less then four stone exists.
GM mays feel free to ignore the doesn't work below normal mana aspect of the item as unless it was at Power 20 that would be true anyhow.