Just get truesight.

I don't want to have to "take" anything, I want to have it always on every unit.

Originally posted by Eggon:

HI, I was wondering if there is a mod which would always show true strength of armies that are visible? Marching towards a resource guarded by seemingly weak opponents just to discover they are much stronger is one of the most irritiating features of this game.

But... it's real feature - some units have "camouflage" ability (like "forest camouflage") and they truly invisible on global map while in forest. So you have to come close to the stack OR have truesight ability on hero or unit to see them from afar.

As a result, in some cases some unit can truly be invisible till you come close to the stack.

Idk about the mod, you can try to search words like "camouflage" or "truesight" in mods section.

Just assume any time you see an obviously under-strength stack it's got some invisible units, particularly if it's in forest or water terrain.