high amp battery isolator

i am looking for an inexpensive battery isolator to handle my 200 amp alternator.  i have a yellow top up front and one in the trunk for the amps as well as a batcap 800.  any suggestions would be appreciated.  also, would you recommend 0ga wire or would 4ga be suffice?  thanks guys.josh

If you just want to isolate the front from rear when the engine is off, you can use a solenoid which should run less $50. Because of the distance I would go 1/0ga. It would run plenty of power for future upgrades.

i thought the same thing.  i had done that with a stinger 200 amp relay type isolator and 2 months after my prorate warrantee was over on my yellow top up front, it took a crap on me as it will still hold voltage, but has no cranking amps.  the tech at optima told me this is because of the long run of 4ga wire between the batts.  he said that the two of them being hooked up in parallel makes them technically a "battery pack".  and that long run of wire between them will make the one closest to the charge source become overcharged and significantly shorten its life.  he said to make this system work properly, you would need to have both batteries next to each other and connected with the largest wire possible or preferably a solid brass/copper bar.  so now we all know not to make this mistake.josh

It's not as bad as he made out, some charging systems seem much more forgiving for this setup. If you want to the way he is recommending, you will need a battery isolator. You will probably find the best selection at camper stores. They are just huge diode packs. The alternator goes to one terminal, then there is a terminal for each (two) batteries and there is another I think it's for a combined power source. I don't think they handle very high amps though. There is a difference I think he's over simplified. Cells contain the energy, it takes several (2 or more) cells to make a battery. The cells can go bad for a number of reasons. Internal shorts and internal resistance can cause significant issues with multiple battery systems, perhaps the resistance of the wire added to the discharge, but it should only occur while the batteries are joined. Over charging, I don't know how to cure, but a big wire should do the trick. The problem being that the battery in the back is drawing current, and the battery up front is fully charged, so the alt continues to charge the front battery to get the rear up to snuff. The simple solution would be to use two batteries of the same type, manufacture, age and condition. I don't know how that battcap works into it, but I'd suspect the two batteries had some differences as well. Also I am not so fond of optima after my experience of two dead new blue tops. The third was finally good and solved my problems.

"If you want to the way he is recommending, you will need a battery isolator... The alternator goes to one terminal, then there is a terminal for each (two) batteries and there is another I think it's for a combined power source. I don't think they handle very high amps though." Don't handle very high amps! They are design for batteries! Most models are rated at 240Amps continuous. The fourth terminal is not a "combined power source". It is either for a three battery rig or a GM voltage sensing terminal. The downside is you will loose a volt or so through resistance of the diodes. "If you want to the way he is recommending, you will need a battery isolator." You can still use a relay in the recommended config. And Yes you should upgrade to 1/0 AWG. The 4 AWG should have never been installed with a 200 Amp Alt. www.wranglernw.com has a kit you can buy and shows you visuals of what needs to happen.

Why do you have the second battery?

the second battery is to supply a large amp to power my mtx thunder 9500 12s plus my four channel amp for mid and highs.  and just to clarify to all who are trying to help, i did have 0ga going from the alternator to the front batt, then 4ga to connect to the rear set up.  i thought this would be suffice as i tested voltage at the rear and it never dropped more than half a volt compared to the front.  im still in need of a supplier for an isolator so if anyone could direct me to a website or dealer where i could get a decent deal on one i would appreciate it.  thanks.josh

Buy 1/0 AWG, Welding cable is the best. Big 3 Loose the BatCap. http://www.bcae1.com/battiso.htm *Pay attention to the fusing