actualy dimming can hurt your amplifier and subs! depending on the voltage drop.... for instance i had a Orion D2500, and with the voltage dipping under 11volts the amplifier would fry! went thru 2 of them that way before upgrading my alternator for a highoutput unit and then never fried anymore amps



but if you want more power for your System.... then buy a highoutput alternator. i think like 150 or 160amps is the highest you can get for a civic.... but still TWICE as good as the pathetic 70amp stock alternator!!!!!!
ill advise upgrading to a stronger alternator if your battery is in good condition.
the battery just holds power... the alternator MAKES power.... id buy a highoutput alt before ya buy a second battery cause tho it may sound VERY EASY to to just slap another battery in you HAVE TO THINK ABOUT A POSIBLE SHORT POSIBILITY! this means instead of using a SIMPLE one main fuse you need 2 if not 3 main fuses!

it can get expensive with the small things..