The game has an automatic replenishment of equipment and ammunition.
When you buy any equipment and ammunition, the auto-refill function will appear in the corresponding sections.
All equipment and ammo in the game are consumables which, when used in battle, must be reacquired after battle.
If autofill is activated, equipment and ammunition will be automatically replenished after battle.
Ammunition will be replenished only to the values acquired before the battle. For example: you bought 30 shells from a possible 45 on a unit, used N shells in battle, after the battle the number of shells will be replenished to 30 units from a possible 45.
If your units have auto-replenishment turned off, then the shells and ammunition will not be replenished after battle. All equipment and ammo will need to be purchased manually.