most car shows have hook ups for power... i've seen ppl b4 plug in a battery charger and just leave that on thier cars with the key turn for the show...
You're supposed to disconnect the battery, and use a power supply for the 120V AC to 12V DC conversion.
I use a 40 amp 12V power supply, it's enough for all my lights and even the head unit (but no subs). Add up the total current draw on the stuff you want to use at the show, then get the appropriately sized power supply. Good ones are expensive, but worth it. Mine came from Ebay.
you could also use a battery pack or some sort probably... That what I used to used for my xbox before I had a power inverter
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"Louis, you better watch who you call a child. Because if I'm a child,
that makes you a pedafile, and I'm not gonna stand here and argue
with a pervert" -- Peter Griffin