When do you use a 'potion of rage'?

[City Builder]

Hey,

When do you use a potion of rage if you manage to buy one or get one in some other fashion? I've not found a way to use it after the battle starts, am I supposed to use it prior to battle?

Also, in the Orcs enhancement campaign for AP, I'm on that little red boat and there are tons of red bottles floating around in the ocean, are they just decoration or are they somehow obtainable?

Thanks,