I have a capacitor that I bought off of ebay not too long ago...didn't really help. Sometimes my lights would flicker/dim then other times it would be fine.
After I put in my JL 1000/1 V2, everything was fine hahah it has the "Regulated, Intelligent Power Supply system" which according to JL, "As your battery voltage fluctuates while you drive, the Regulated, Intelligent Power Supply™ system maintains steady, consistent power at any impedance between 1.5 and 4 ohms and at any voltage between 11 and 14.4 volts."
get a good battery or dedicated battery such as oddysey drycells, and do the big three. you should be fine imo