Max % Defense

Couldn't find this via a search, but what is the max % defense you can have for your tower? The numbers suggest you can get to 100%+, but I doubt that's the upper limit, or, I calculated something wrong.

Defense Upgrade: 49.5 Card: 11 Lab: 5(?) Perks: 25 (maxed perk upgrade?) Chrono Field: 20 (maxed lab upgrade?)