Adding 2nd battery

you need to purchase a isolator, and the battery and some wire.....the isolator will usually have instructions on how to and what you will need to install the second battery.Quad L Handyman services

No disrespect to Ketel, but I think you are saying you want both batteries to be parallelled to power the system, both at the same time... Is this correct? If so, then you must forego the isolator, otherwise, you will be in the same situ as you are in right now... not enough power to run the system. If you are going to bypass the isolator, you must be certain that your batteries (front AND rear) are new, and identical, so they will charge equally. Any battery shop will tell you this is true. If you do not take this step into account, you will overcharge or undercharge one or the other, or you can have one discharge through the other... generally not a good thing. You will also need to be certain your alternator is beefy enough to keep two batteries topped off. After these steps are addressed, if you have an additional input to your power distribution block, simply plug the positive of the new battery into that input, and the negative post to the chassis... Done. I have done this more than a few times, and this is the recommended method by the battery shops here in town... You will notice there is no isolator in my system. 2001 Honda Civic LX Eclipse 8051 E8 deck Eclipse 3122 driving Infinity emit Kappa tweeters 80w X 2 Eclipse 32440 driving Eclipse 89940 Point source 6X9's 120w X 4, bi-wired, bi-amped Eclipse 34230 driving Morel MW-162 6" midbass in doors 370w X 2 Eclipse DA7122 driving Eclipse SW9122 12" Titanium sub 1350w X 2 RedTop Optima 12v under the hood 2 RedTop Optima 6v in trunk, one each side wired in series 2 Rockford Fosgate 1 Farad caps on custom hand built power bars Alterstart 165 Amp alternator with Datel 150A Current Shunt and blue LED meter for monitoring current outputIt all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

OK, guys... let's let it go... I was not afraid of attacking anybody. It's all over now. I said that like that to cover *MY* ass, sometimes I come off a little brisk in type. In person, I am very easy to get along with, but I have difficulty typing a point I want to get across, without sounding like a know-it-all. I do know a lot, but so does everybody else here, and we all want to be heard. This is a great forum, and it will continue to be so, as long as we all agree to disagree. Whoever it is that thinks they are being attacked, be the bigger person and let it go, without a "I'm beig attacked" response, and let's get back to the forum we all want to enjoy.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

If you think your system is pulling too much power, a high-output alternator is the proper answer, not a second battery.Support the12volt.com

I agree with DYohn on this. You need that high output alt to get things going. I run 2 batts and a battcap, but I also run a 200amp alt. I don't use an isolator. There is no need as far as I can see. I have had not trouble at all. My buddy has a UD roll back wreaker that has 2 batts from the factory with no isolator. My other buddy drives a kenwoth with 6 batts and no isolator. Just make sure you wire them correctly, if you can't see a pro.Big Dave

One question to ask before adding a second battery... Will the system be played mostly with the vehicle off or on? A second battery becomes a load with or without an isolator, actually due to the resistance and loss of the diodes in the isolator you are increasing the load on the alt.(not a huge amount) Hense the heatsink on the Iso to let off heat. Wasted heat and voltage loss across the diodes. Emergency vehicles still use this type of setup. Many folks here agree a contactor, or relay, is the best meathod to isolate 2 batteries. One advantage is installing a switch to connect the batt's together if the main starting batt is dead. Less loss of voltage and heat using this meathod. Cheaper, and easy to install. Anyway, if you are going to spend hours listening with the vehicle off a second battery is worth your time and money. If you are going to listen mostly when started, a few 1 farad caps would be helpfull. Caps are nothing more than storage devices. They can't make energy or magically solve other problems in your system, but they can release large amounts of current quickly and keep your voltage steady during peaks. I think everyone would agree a H.O. Alternator is the best investment, no matter how many batteries you have or how they are connected. Also keep in mind with gas $$$ that an additional battery will add 40 + lbs you are carring around with you. I'm running Zapco C2K-4.0, C2K-3.0, C2K-6.0 in a 03' F-150, all with the stock battery, stock Alt. and a few BatCaps. Some dimming if the A/C is cranked and the Headlights/Driving lights are on. Voltage at the amps is 13.9 when started. Large guage power cable helped here. Next step is a H.O. Alt. Good Luck!

As Speedway noted many HD Work vehicles and Large Trucks have multiple batteries as standard equipment without Isolators or Relays. These vehicles need huge reserves of current to start, not operate. A 500hp Deisel motor needs some serious kick to turn over! When these batteries are replaced the manufactures highly recommend all batteries be replace with the exact same model, type, and age of batteries. Truck batteries are not deep cycle type. Very high CCA ratings though. An Isolator would only really make sence on these Trucks if you had say an Invertor and wanted to run it with the vehicle off. Ambulances and similar type vehicles seperate batteries to insure available power for medical needs etc. The Alternator is suppling the current to the load not the batteries. The bats supply what the Alt cannot durring peak demands and provide filtering for the electrical system. In cold weather try to start a Volvo 770 on less than 4 batteries!