Research your country's copyright laws and their requirements on public performances. I don't think anyone of us here is qualified to speak on behalf of the Swedish Government.
If you plan to power any system using a car battery I'd recommend a Marine battery vs a automotive one... for a couple reasons. 1. It's more suitable for exposiure to the elements and 2. They tend to hold their charge better. The later is my understanding and could be completely wrong.
No matter how you approach this you're going to need to either use just one self powered speaker or two very efficient ones otherwise you'll run your battery down in a matter of just a few hours of use.
If you plan to power any system using a car battery I'd recommend a Marine battery vs a automotive one... for a couple reasons. 1. It's more suitable for exposiure to the elements and 2. They tend to hold their charge better. The later is my understanding and could be completely wrong.
No matter how you approach this you're going to need to either use just one self powered speaker or two very efficient ones otherwise you'll run your battery down in a matter of just a few hours of use.