I can confirm this, flaviojs. With 6 peltiers and invis9 I was able to easily stack 2 and a half hours of invisibility. Even submitted a patch to show hours.

I suggest multiple changes:
1) Make peltiers not so super awesome. Reduce cooling rate increase from 3 to 1 per second.
2) Make invisibility costlier. It should be a mid to late game spell, so e.g.      -    cost = {base = 45, per_level = 10},
+    cost = {base =100, per_level = 20},
3) Make most 600+ class bots see invisible tux. Perhaps with a delay, with the delay depending on bot level.