Guys the best reason i would be able to think of that you had to upgrade during battle is that you dont like send 1 titian or something else that can kill very easyly in the beginning of the battle.
Cant beat chapter 17 "the end" is too strong and i kinda finished the castle quite too fast so all the black dragons and the angels where with "the end"......so i lost badly.
 "Hero's Arms"){kind=icon}
 "Epic War 2"){kind=icon}
 "Super Energy Apocalypse : RECYCLED!"){kind=icon}