Hi there dude how's it going?
Quick question: what's the overall power of your amplifiers? First and foremost, a dual battery setup should be a last resort option. Before even considering one, you should upgrade your existing battery and existing grounding cables. Not only will it save you a hell of a lot stuffing around, but probably some money too.
I'd recommend to you an Optima Yellow Top (D34 i believe is the model no.) or Optima Blue Top battery (D34M). If you know where your looking these can be had for around $315.00 for the red top and $335.00 for the blue top after postage. The former is deep cycle, 750 CCA and has a reserve of 120 minutes. The later is exactly the same as the Yellow Top , but on the battery has two more physical smaller accessories posts which also come in handy if you later on want to chuck in other electronics and connect em up using simple ring terminals. So what's it mean? Deep cycle battery - means you can fully discharge and recharge it over and over again without causing the damage you'd cause to a regular battery. 750 CCA - (stands for Cold Cranking Amps). Pretty much the higher CCA you can get the better. Take a look at the battery you have in there now and i bet you'll find it's at most 500-550CCA and probably lower than this. Once again, reserve capacity, the longer time you can find the better.
You can find batteries with higher than 750CCA, but i suggest the Optima because you'll be hard strapped finding any other brand or type apart from possibly an Odyssey that puts out that much power while still maintaining a compact design that will fit in stock under the hood (i.e. no other modifications necessary). Both Optima and Odyssey do make more powerful batteries, but as said, these won't fit straight in without you having to either make some significant modifications under the hood or relocating it to the boot. Check out
www.optimabatteries.com.au for more info on the optimas.
Upgrading grounding: the simplest and cheapest power upgrade you could ever do. Simply run another run of 4 gauge or 0 gauge cable from the negative battery terminal to the chassis ground where everything else already grounds (your looking at around $15-$20 for half a metre of 4 gauge and a few ring terminals). This will in many cases be enough to stop the tell tale headlights dimming with bass hits etc.
Other simple advice would be to make sure you have strong connections both at the battery and that your amps have strong ground connections. Also make sure they're physically clean connections (i.e. clean away any dirt and grime/sand away paint before attempting to ground the amplifiers so that there's a solid connection).
If you do these things, there's a very small chance you'll have problems with not having enough power. There's a general concensus among car audio fanatics that capacitors look pretty but are useless, so don't let the store guy con you into buying one. All in all, the best thing you can do for your charging system is to upgrade everything that's there and make sure it's all good before you even consider going to a dual battery setup. Alternator upgrades are another option, but once again, your looking at a significant amount of money for a very small increase in power and having difficulty fitting higher amperage aftermarket models that weren't made to suit said vehicles specifically. Alternators can also be re-wound for higher amperage, but doing this has other disadvantages over buying an alternator originally made to put out more power.
At the end of the day, tend to your battery and grounding system first. It should solve your issues for you unless your planning on using very large amounts of power (and i mean quite large indeed). Hope this helps, cheers, Bryce.
