When technicians retrieve their turrets, it automatically fully repairs and reloads the turret without needing or using any ammo packs or repair charges. This gives them infinite ammo.
Oh and additional note to this. There is also a bug, that turrets don’t require ammo when they are equipped in the first place. They have ammo packs, but don’t need them. Currently the ammo packs are only required for technicians to reload a currently deployed turret.