The key to any battery-powered sound system is efficiency
. Home and car sound gear is not designed to be efficient or light - it just isn't a concern in those applications. Low efficiency means you need lots of power to make the same amount of sound, and lots of power means a big heavy amp, a big heavy car battery, and maybe a big heavy inverter too. An efficient speaker can produce 5x
the volume from the same amount of power. An efficient amplifier is 2x
better than a standard one, plus its far smaller and lighter. Together this means that with a bit of attention paid to your component choices, you'll get way more output for the same amount of power.
Lets take a look at Deep's current system. He's got:
2 nice Yamaha powered speakers (they have a built-in amplifier)
An inverter because the Yamaha's need 120V
A car battery
Another option I see some people using goes like this:
2 big auto-sound speakers
a big auto amplifier
a car battery
Either way there is a lot of inefficiency. Using 120V powered speakers, the amp inside the speakers is moderately efficient (not the best, not the worst). we lose a good chunk of efficiency because of the inverter.
With auto-sound gear, you don't need an inverter but the problem is that it all the parts have very poor efficiency. I think this is due to marketing forces at work - the folks selling you this stuff learned that if the amp and speakers are bigger and have higher watt ratings, they make more money selling them. but, those high watt ratings are only needed because the gear is so inefficient.