2 batteries or 1 yellow top only

I have done the big 3, + H.O. 160 amp alternator ( about to get it re-wound to 200 amps ) through a friend at a shop that does that. Head Unit Soundstream VR 450t ( t means TV tuner built in ) Pre-Amp Equalizer: MPQ-4US Amp 1: Alpine MRD-M1005 powering 2 Cerwin Vega 15"s Amp 2: Old Skewl RF 301m mono amp powering my 6x9's and 6 1/2's and soon some 4x6's and 1 in tweets, have yet to purchase the last 2 sets of speakers for the dash( i like mono sound from my front end, I am weird, i know, IDK why) now for the question at hand, i currently have an autocraft battery under the hood PN 34/78-4 CCA 800 CA 1000 Res 115 I just purchased a Yelloy Top d75/25 CCA 650, CA 810, Res 98 should i just replace my battery under the hood with the yellow top, or should I mount this in the Yellow Top in the back, isolated of course from the main battery, i don't think venting would be much of an issue, i have a 2001 Chevy Blazer, with the 2 vent shafts in the plastic, on each side of the rear hatch glass, or should i build a vent hood? I guess that would be a 2nd question to any one knowing the topic and these YT batteries and 2001 Chevy Blazers if having the YT in the rear, as a 2nd battery is the best option, i will never buy a capacitor again...lol, So how should I approach the battery situation, YT under hood, or as 2nd battery? What venting would I have to worry about / how would I do it, for the YT in the back of my Blazer which has 2 vent slots on each side of the "hatch", If i even need to worry about venting.Brain

can anyone out there give some advice on the battery subject please??? befors i order parts i might end up not needing...LOLBrain

Too late - you purchased the Yellow Top! You can read what others think about using Yellows as crankers. (IE, you may find Reds are suggested, or that Optimas are not.) IMO for an audio setup, it's best keeping a wet-cell as the cranker and fitting a 2nd battery near the amp. That negates the use for a capacitor and - with an isolator - allows the audio to run with the engine off without effecting the main/cranking battery. For SPL, even though floodeds (wet-cells) are usually the best, some use AGMs to avoid the need for venting. (Local die-hards add vented enclosures.) Note that Optimas are AGM batteries (Absorbent Glass Mat, aka VRLA = Valve Recombination Lead Acid) and hence - under most applicable vehicle etc Regulations - do not require venting. (IE - they do not have to be enclosed on a sealed vented (... to the outside...) enclosure. Hence you should not need to worry about extra venting. (IMO an AGM is more likely to melt or explode than cause external hydrogen ignition.) Dual-battery set ups should have an isolator. If you have a charge-light circuit - ie, a alternator (regulator) with a D+ or L terminal - IMO the best isolator is the UIBI - a normal relay that is triggered by the D+/L circuit. Otherwise a voltage-sensing or aka "smart" isolator. The isolator (relay) is inserted in the normal twin-fused battery interconnection - ie, batt#1 - fuse - isolator - fuse - batt#2.    Note that the above isolators are automatic. The UIBI only connects when the alternator is charging. Voltage sensing isolators are supposed to behave the same, but in practice have turn on delays, and often turn off delays (namely till the battery voltage drops below a certain level - eg, 12.5V, 12.7V. 13.2V. 13.5V etc depending on model).    You can also use manual switching - eg, a relay controlled by IGN+12V or ACC or a switch. But if you leave IGN or ACC on, or forget to turn off the switch.... Also IGN+12V means paralleled batteries during cranking. Whilst sharing cranking current may be good, the interlink relays and fuses and cable have to handle it. And interconnecting a full to a flat battery (when not being charged) can have its problems or hazards. Note that the UIBI is just a manually controlled relay but with its coil connected to D+/L instead of ACC or IGN or a switch. Note too that not all alternators (D+/L) may be able be able to energise all relays. In such cases, a transistor or MOSFET or a smaller relay can be used to buffer the isolating relay. The same principle is used to increase the current capability of the isolator - eg, if you want a 200A isolator but only have an 80A (voltage-controlled) isolator, use the isolator to energise a 200A or 300A relay etc. (That's much cheaper than buying a 200A smart isolator etc.) I don't know the power demand of your audio system. The above is for big amps in the boot, er... trunks, and would be pointless for HU amps or internal amps - unless wanting to run for extended times without the alternator. The only addition for BIG audio systems of ~3kW etc would be a cap to protect the AGM if extra AGMs cannot be added.    That reflects that AGMs do not like supplying big current. Though they can, it does damage them. (And I'm talking current peaks etc - not "within spec for a given lifetime" currents.) And the above reflects why wet-cells should be used as the main cranking battery. I hope that helps. I've missed certain basics as well as detail, but a search should find more (eg, google "uibi" or "uibi oldspark" for what UIBI means and why, adding manual controls & low-voltage cutouts etc).

Old Spark,      everything you have told me verify's my thoughts on the subject, i was just looking for further opinions, the plan is to put the YT in back, with a smart isolator, and i also know the pre-isolator relay setup you are talking of, right now, with the audio, external and internal effect lighting, and mods, and security sensors i have, i have installed a relay panel in the middle console and have 5 relays currently, and space for more as needed on the other side of the armrest inside on the other side, ready to drop in more relays, as i already have it planned for the future and have the mounting board for 5 more on the other side Again, thanks for your input, as I say, it seems right along with what i was thinking. Brain

The D+/L triggered relay I mentioned is not a pre-isolator, it is THE isolator. Either use it or a smart isolator, but not both. And if you can use it, there is no need for a smart isolator except perhaps if modifiable as a low-voltage cutout (which few are). And I suspect that the type of relay/isolator you require won't fit in a relay panel. Depending on the amp output, I'd assume a 100A relay or larger.

here is the relay / isolator that i was considering, it has great reviews, both on their site, and other places also like amazon, and review specific websites, as far as i can tell, this is exactly all that i would need in one package. http://www......com/item_28364_The-Install-Bay-IB200.htmlBrain

So you're going down the UIBI route? Not that links to eBay etc work on this site, but that IB200 is merely a relay. And I'd expect few alternator regulators could energise it directly.

well, that was only my first item i saw on sonix electronics that i thought might do the trick, which is where the link should have taken you to, guess links are not allowed, although i use this site a lot, i rarely turn to the forums, what other ones would you reccomend, i do have a High Output 160 amp alt v.s. the stock 100 amp alt, but I am about to get the alt rewound locally by a friends shop for next to nothing up to 200 amps, this is the first time i have ever considered dual batteries, if you could recomend some different options for my setup, that would not break my bank, it would be much appreciated.Brain

I'm not not recommending it. I'm merely pointing out that it is merely a relay. It has no automated switching function - you have to supply the means to control it. I've already said what I think is best - a charge-light controlled relay, aka the UIBI. But that assumes you have a charge light circuit on the alternator (or rather, its regulator - especially if that's separate to the alternator), but most alternators do except for the newer DP or ECU-controlled alternators, though there may be some other "is charging" or "is not charging" indication that could be used, if not other outputs from the alternator. And it assumes you can set up the required control wiring to the relay, maybe with an smaller intermediate relay (or transistor etc) if the alternator (regulator) is unable to supply the isolating relay's coil current. Otherwise it's a case of using a voltage controlled isolator - sometimes called a smart battery isolator etc. Both the above can be used to drive a bigger relay. EG, a 30A UIBI or 80A smart isolator can instead power a - or several - 200A or 400A relays etc. Alas I'm repeating myself! As to how to size the cabling and relay required... The worst case is the maximum recharge current that the battery can draw plus the maximum load it will supply. In practice it may be less than that since very high battery recharge currents may only last tens of seconds, and normal transient ratings (ie, thermal capacity of relays, cable & fuses) may cope. Or it may be less because your 2nd battery is never that flat, or not flat with a (high) load, etc. But the UIBI is logically cheaper than a voltage-sensing isolator since they have the same relay, but the UIBI does not require the complex voltage sensing circuitry.    Be aware too that your rewound alternator may not be overly reliable. Even if its power diodes are appropriately rated or upgraded, the alternator is unlikely to have the same thermal capacity (and hence a lower transient capability) than a purposely wound alternator.