Other option is getting a Deep Cycle Battery or two and running them in an isolation circuit. When one battery runs out, replace it with the other and charge the first...that's pricey as well, unless you know someone that can get you Optima Yellow Tops for about 80$ (I wish I knew my friend could before I got my red top!)
oh...and that "Pricey" Object up there will only provide 35A. That won't run everything that you want it to. It wouldn't even run the small system in my car, I believe...
if you do runs this route dont expect to be hit you subs with this the unit itself will just overload and shut off. it should turn your tv an things on look around first. there are some battery chargers for you car the are made to jump cars and you could just connect it to the terminals and plug it with like "charge" the batt ive seen that work.
what most people will do when they need a charge without starting their battery is get a high ampere battery charger that way they can charge it fast. you will see this at alot of auto sound competitions.
When a battery is depleted, replace it and charge the first ... This is well.there pricey some of your car battery charger jumping, you can connect it to the terminal blockage likecharge "of the cotton I've ever seen.