Mon Aug 15, 2016 3:47 am
Experience and promotions are separate things.
To get a promotion your leader has to be a) promotable (not all leaders are) and b ) have gained four places of seniority. You gain seniority by winning battles, and you have to win them big, i.e. gaining NM by destroying elements. A good way to farm promotions is by besieging then assaulting smallish garrisons (a couple of militia aren't always going to move the needle). Your leaders can lose seniority when they participate in losing battles.
Experience comes from participating in battles. Obviously you gain more when you win, but they still gain some AFAIK even if you lose. As your leaders gain experience they earn stars, which increase their OFF and DEF stats. Leaders cannot lose experience. (I would not 100% trust the info in the wiki link above, experience is an area that underwent some changes in CW2. For example, you can now view current XP totals in the element window, and the number of XP needed for the next star is fixed not variable, and is also displayed. Furthermore, I believe that elements that receive large numbers of replacement hits CAN lose some XP.)
Individual elements also have experience, which affects their stats. As they gain stars they become more effective in combat. Once a conscript, volunteer or militia gains his first star, he then has a chance each turn to automatically upgrade to a better element (conscript to regular, for example) at which point some or all of his experience is reset. Unlike generals, elements have the potential to gain XP even when not fighting, 50% chance per turn to gain 1 xp if memory serves. If they are in a stack with a Training Master (HQ units have the Training Master trait) they gain 1 xp every turn on top of the one they may or may not gain for free.