I just bought a 3000 watt continuos power inverter and am running a portable air conditioner that has 840 watts.Well ...its works for about 5 minutes ,then shows a low voltage reading.Does this mean the battery in my my ford windstar is not powerful enough?...do i need to buy a bigger battery with more amps?

I want to build a speaker tower all powered by the Dayton Audio MCA2550E 2.1 Channel Class D Amplifier. I was just going to build in a pair of the Dayton Audio B652 6-1/2" 2-Way Bookshelf Speakers directly to it. I was going to use the sub output on the amp to power a Goldwood GW-8024 8" Butyl Surround Woofer at the bottom of the tower in a sealed box. Will all of these together make a a tower that can produce a decent amount of sound at high levels? Or will that amp have trouble pushing ...