Upgrading units.

good idea but no.

No.

There is no way to heal unit in the game except time and it is fine like this. Else, I would use units until they have only a few HP left, THEN upgrade them. Totally unrealistic /counter-intuitive.

If there were to be a means to heal units, I would think it best to manifest as a buildable field triage unit and maintenance battalion that effects the stacks that they are a part of, increasing the healing performed when a day ticks over by an ever increasing percentage as they are further and further researched. However, since unit healing is tied to gold, I doubt we'll see such a thing.

Imagine one infantry unit with lets say 500 man, it is on 50%hp witch means there are 250 man left, by improveing their equipment you wont incrise number of man, you will only incrise stats and hp of those 250 who are left.

There is your explanation.