Battle Territory bonus can be found on a cell marked with a gift box icon on the world map. It appears twice in every zone and awards an X amount of maximum Trimps. The default amount of maximum Trimps awarded per gift box is 5, however, that amount can be increased with the Trumps perk.
The bonus to maximum Trimps from the Trumps perk is persistent and stays even if the player uses a respec. It is possible to invest heavily into Trumps, then respec at a higher zone while keeping the additional population.
Battle Territory bonus is also affected by the Carpentry perk.