two batteries

OK.... I have a 2008 GMC Canyon I am installing a Kicker 1000.1 and a Kicker 350.2 amp. I am installing a Kinetik HC1400 or HC1800 (depending on which one will fit). I am anticipating the need for a secondary battery as well. I read on here (searched and cannot find it) that somebody bought a Walmart battery and wired it up as a secondary battery. I was looking at a Kinetik HC600, it'll fit perfectly behind the seats. I have no plans to run the system without the truck running. Can I do it with dissimilar sized batteries? Do I wire it up like I would a cap? Do I need an isolator? Thanks again.

Two batteries is not going to do much for you if you do not plan on running your system with the truck off like you said. If you have power issues then you should look into getting a high output alternator and big 3 upgrade. An upgraded battery (over a stock battery) can have some benefit but the alternator and big 3 are going to be FAR more beneficial. A second battery will just put more of a demand on your electrical system which can actually worsen any power issues you may be having. If you do run two batteries you will want to make sure they are the same. They should be EXACTLY the same as any small differences can lead to shortened life of one or both of the batteries. You will wire them in parallel and do not need an isolator.

Agreed that batteries will not change insufficient supply. Ideally the alternator will supply sufficient power to handle all loads. As above, if paralleled, batteries should (must!!) be matched, but IMO it still shouldn't be done without safeguards. And with 2 matched batteries - one in the engine bay and one elsewhere - they will no longer be matched. Besides, eventually one will start to fail and that's when the problems begin - especially if they are AGMs! Instead, for 2 battery setups, the AGM should be with the amp - close enough so that a cap isn't needed.    The main battery can be retained. The audio battery is only connected to the alternator (or main battery) when the vehicle is charging. Exactly how depends on various capacities (alt, amp, battery(s)). However added batteries (even caps!) do not "add a load" to the electrical system - in fact they tend to take the strain off the alternator etc. There may be added alternator load to recharge them, but that does not strain the alternator. Besides, that is returned by the added battery capacity during discharge. And since the battery discharge voltage drops will be lower, that means less charge current per battery.    Just remember, batteries and capacitors do NOT magically generate power. (They are stores for power after being charged.) Alternators generate power (via fuel conversion) to power loads and charge storage elements.

Hmmm... OK. Thanks guys. I thought that thats what the HC600 was designed for, to be wired near the amps like a cap would be.

Ahhh.... found it. Heres the thread I referenced. https://www.the12volt.com/installbay/forum_posts.asp~TID~119473~get~last This is what I wanted to do.

oldspark wrote: However added batteries (even caps!) do not "add a load" to the electrical system - in fact they tend to take the strain off the alternator etc. There may be added alternator load to recharge them, but that does not strain the alternator. Besides, that is returned by the added battery capacity during discharge. And since the battery discharge voltage drops will be lower, that means less charge current per battery.

I agree with most of what you said but this point I think I have to disagree with. A second battery or cap is going to have a some internal resistance. More power is going to be going to it then is going to come from it as no device is going to be 100% efficient. Although the amount of power a cap or battery may actually use is very small it is still less than what you started with. So basically your alternator is going to need to produce more power than it would without these devices which is why I say it is more of a "strain". A battery is going to need to be kept charged so having two batteries will have mean now the alternator needs to keep two batteries charged over one. This is not very difficult when both batteries are fully charged. The problem can arise when your batteries are drained. If you are running your stereo and the alternator cannot keep up with the demand your batteries will be constantly drained. Now you are asking the alternator to charge both batteries and still keep up with the regular demand. This will mean a much larger demand on your alternator. So in some cases the strain can be great on the alternator.

Tommy's reply has good info. I do not like the diode splitters for various reasons, but they have their application. But it may cause undercharging of the battery(s) and a lower system voltage. And with the wiring in the fuse 2 battery setup, keep in mind the likely lower charging rate of the 2nd battery, but ignoring wiring losses it will eventually charge to the same level at the first battery (just slower). Can't say the same with the diodes however - although both battery voltages depend on the two path resistances and loads in both cases, the diodes probably exhibit a greater voltage drop with increasing current.    WhiteRod - such resistances have little effect. A battery's & cap's internal resistance is usually way under 0.1 Ohm. Negligible. (The equivalent of a 12W bulb if across 12V - not that it is, but more later.) The battery's float current is about 1% of its rated AH current, so that too is negligible. For a battery, it is actually its charging inefficiency that is the biggest "extra load", but that is only after a discharge which means it has supplied power that the alternator hasn't. IE - it did REDUCE the load on the alternator. And as I pointed out elsewhere, the initial total recharge current for two batteries may be less than with one. Why? Because the discharge voltage is lower, hence lower initial recharge current. In simple theory, the recharge current will be the same for one battery as with 2, or 10. But batteries are not linear, nor simple. [But caps are - do the calcs and see the difference - the only "extra" power is the current through the caps ESR which is typically 10 milli-Ohm - a mere 100W for a few seconds if the cap can take 100A!! Not that caps are (or need be) used in most decent systems... And a battery won't absorb 100A (for long, else shouldn't!)] So the extra "strain" on an alternator is a few percent. The "strain" it saves the alternator can be much higher - ie several times the altenator's rating.    But the point is - ignore stuff about the extra strain of more batteries and caps. If that were a concern, we would all be using the smallest battery we could. And probably be using hand-cranks too! PS - a almost embarrassing omission from above.... Of course any added resistance such as ESR REDUCES the current in the added component thereby reducing its "load" on the system. IE - ESR etc reduces loads - it does no increase them. But I did go on to explain "the real situation". But any argument that uses ESR or added resistance as an "added load" argument can be dismissed (it's the opposite that is true!).