big 3 with more than one battery

i aware of the big three upgrade but i was wondering if you had multiple batteries in the trunk or and extra under the hood can the big 3 be done on the second battery . also how is this done. on the alternator to battery do i add on power wire with a distro block and split two wires to the batteries. same as the alt  to ground would i double that or leave as is. on the batteries i would assuming upgrading the ground but wwounldnt that make ground loops and cause an issue.

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1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"

big three is the wiring under the hood...as for the batteries in the back...you can run a 0 gauge ground from the front battery to the back as well as grounding the back batteries to the chassis

That's true but wouldn't that make it at 24 48v system. That also could mess up your 12v devices. So would you need a isolator or relay to seperate the batteries

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1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"

No it will still be a 12v system if you parallel the batteries.  The two 12v batteries do not "add together," save for ultimate discharge capacity.

Are you using the same batteries?

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"I'm finished!" - Daniel Plainview

The batteries remain in parallel and this leave you with a 12v system. Do not wire them in series which would get you a single 24 volt battery. The isolator question depends on the type of batteries and alternator you are using and the way that you intend on using your system. What are you trying to get out of your charging system. More time with the engine off? More available power near the amplifiers? More cranking time? Your charging system needs to be tailored to the demands it will be placed under or you will end up spending a lot of money on parts that might not get the job done. In the event that you are attempting to give your amps the most available power then an isolator is not likely the solution. Post the part numbers of your batteries the amprage of your alt. the year and model of your ride and your intended usage of your charging system and you will find better answers.

I was thinking upgrading the alternator and adding another battery for more system when the engine is off

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1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"

In that case you will most likely be happiest with the following.
1.     the smallest battery possible that is still suitable for starting your vehicle. This battery should be a lead acid type and will only function as a starting, and engine management. You do not want a deep cycle here. All other electronics will be connected directly to the second battery.
2.     A larger second battery should be a deep cycle dry cell. This battery must be a deep cycle in order to withstand the abuse of being used extensively with out the engine running.
3.     A high amperage (200) relay to disconnect the starting alternator from the system when it sees no ignition (engine not cranking or running).
Your starting battery needs to be up to the job of starting your ride reliably but should not be over sized. This battery will put a high demand on your alternator (as any battery will) but you can reduce that demand by keeping its size (capacity) down. Because this battery is physically disconnected every time you shut down your engine any extra capacity that this battery might have is useless to you. But will pose an extra burden on your alternator every time it needs to be charged.
The second battery can be any where from a standard sized Optima yellow top to a kinetic HC2000.
This system is conservative yet robust. You will never have a dead battery when you crank your engine, and you should get a good hour of pounding time with out damaging your reserve battery(depending on many variables that you have not supplied me with).

I do not recommend an isolator or identical batteries for your needs.
Run 0gauge parallel between both of your batteries for both ground and positive.
As far as your alternator goes you have not disclosed the type of vehicle that you have so that is up in the air. The largest your budget will allow for though is a good rule of thumb. Check to see if Summit Racing has an application for your vehicle. They sell decent quality units that are a lot of bang for the buck and easy to install.
     Check out www.kinetikaudio.com

I have a 1986 cadillac deville sedan 4.1L and I got qouted for an alternator from ho alternator for a 220 amp for $589 which I plan to order after I plan on if I decide to got with two batteries or not

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1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"