question about battery

hi, i'm not sure if i asked this before, but here is my idea if i can't get a totally custom made alternator built to when i need it to be, here is my plan, Get to kinetik 16 volt volts and wire them paralle to my sub amp and have my 4 channel amp being powered by my alternator/starter battery. and i say 16 volt batter yes because of the amount of voltage drops and i was wondering how often would 2 Kinetik HC16V batteries last. the sib amp is a md1d

You should be able to have any alternator made that you want. The alternator is always the best place to start IMO. I have read many threads where the battery / alternator / cap is the topic issue, and here is what I've done....
I have a friend who has an ignition shop in Rochester, NY, and I had him build me a Dodge alternator with a HD Ford external regulator, and I mounted and hard-wired it into my 1992 Nissan Stanza. I have 80 amps / 16.7 volts at idle, and 160 amps at anything over 1600 rpms.
My system consists of an Alpine CDA-9885 / 2 Audio Control EQL's / MB Quart and Infinity highs / one JL 13W7 / one old school Punch 4080 and one Punch 200 / one - 1 farad cap.
My point in saying all this is....because it was build the correct way, when I have all my lights on and a bass CD going, the voltage only drops .7 volts. 2 batteries and more caps are not going to give you those results. Granted that I put $600+ into the alternator alone, my electrical system has been bullet-proof for 5 years now....less the alternator bearing of course.

Good luck!....

I don't think the batteries would last that long if you are playing it loud.

Definitely go with a bigger alt if you can and if you absolutely wanted to get a second battery take a look at Kinetic's HC batteries they range from a 600 to 2400 amp source.

get a custom alt. two bat.s would be retarded

Actually 2 batts is a good idea when done right.