I'm not sure I'm a fan of basing the system on consumable repair hammers, unless the rate of equipment degradation were decreased very significantly compared to the current beta. I wouldn't want to have to cart around dozens of hammers just to get through a long dungeon - that's maybe exaggerating a little, but not much, if you'd only get 1-5 uses out of one hammer.
Numbers can be changed.
Another idea, maybe better than a flat "repairs 20%, no matter how much durability the thing has":
Repair Hammers contain 300 charges. Each charge can repair 1 point of Durability. If you have Repair 1, you can use up 60 of the charges, leaving you with 240. With Repair 1, you cannot use a Repair Hammer which has 240 or fewer charges. "Not enough Repair."
Using charges 180-240 requires Repair 2.*
...
Repair 5 lets you use up charges 1-60 (after you use up them all, the thing breaks).
Yes, you'll have to carry around a few repair hammers. Too bad.
