The Wiki says that each point of Upkeep is -5% damage to your eq. 20*5%=100%. I REALLY doubt it works like that, though.

TheWiki Posted:

Upkeep is all about keeping your items less damaged. Whenever you are successfully attacked, your items take damage to their condition. How much damage they take is determined by two things. First is the Quality of the item. Higher Quality items take less damage each hit; but don’t bumume that more expensive items are necessarily of higher Quality than cheaper ones.

The second factor that determines damage is your Upkeep stat. For every level of Upkeep you have (including the first that you start with), your items will take 5% less damage than they would otherwise. At Level 6, then, your items only take 70% of their normal damage.

Bruce Bear will charge roughly 20% of list price (see Frugality below for an explanation of that) to fully repair an item. Even though you can only see damage as an integer, Bruce Bear will charge based on the damage percentage including fractions, so prices may seem to fluctuate by a flezz or two.

http://www.forumwarz.com/spoilers/wiki/Upkeep

Also: The forums need a more robust quote handling system.