Originally Posted by SabreWulf69
Using battery as a capacitor can be very dangerous, as well as the fact of having a vehicle battery in your bedroom, as the amperage is enough to weld a spanner across the terminals. Low frequency wavelengths are longer and slower which is why the bass travels further and sounds louder bouncing of the back of your car boot. As far as car audio is concerned (deadening aside) technical accuracy of bass would be alot better having the sub face towards you, or at least having a more direct, accurate and sound friendly route of the subwoofer's bass as in the Bowers & Wilkins system going toward the front.
I've been using car batteries for over 12 years as well as just about everyone I know - they are perfectly harmless as long as you yourself have a little common sense.
Just like ANY other electrical component / device on earth...
ANYTHING can be dangerous if handled by an idiot :P heck even a spoon can be lethal if you try and swallow it, but use it as intended, and you'll be just fine.