Replenishment is a gameplay mechanic in the Total War series. It is the process in which regiments that are under full strength refresh their numbers.
Empire: Total WarEdit
In Empire: Total War, replenishment is manually activated by a button on the right of the army tab when an army is selected. All regiments, regardless of unit type, replenish in two turns. Replenishment costs money: the heavier the unit's losses prior to replenishment, and the more expensive the unit type, the more money is required to replenish a regiment. Replenishment is generally cheaper than training new units from scratch. It can reduce the experience of a regiment (the new soldiers added are counted as completely inexperienced troops).
Replenishment can only be activated if there are sufficient funds available. In cases where an army cannot replenish and faces an imminent threat, it may be more prudent to merge units, instead. Merging troops instead of replenishing can also help preserve the experience levels of more veteran units.
Napoleon: Total WarEdit
Replenishment is completely revamped in Napoleon: Total War. Instead of being manually activated, it occurs automatically for free, and it no longer always takes two turns. Instead, multiple factors influence the rate of replenishment. Replenishment is denoted by a plus symbol next to the unit card on the world map. The color of the icon determines how quickly the unit is replenishing (red means a very slow rate of replenishment; green is very fast).
The Russian unique building, the Minin Monument, gives a global replenishment rate increase. Buildings such as farms, roads, and especially supply posts boost rates of replenishment. Regions that are further away from enemy regions replenish more quickly, too. Finally, regions that can train a certain unit type allow that type to replenish faster (for example, if a region can train Musketeers but not Silesian Schuetzen, and an under-strength regiment of each rest in that region, the musketeers replenish more quickly).
Units only replenish in allied or player-owned regions, and only when stationed in a town or when led by a general. Certain general traits grant faster replenishment. Units suffering from attrition do not benefit from replenishment.