How to add a second battery
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This is a discussion on How to add a second battery within the Interior Mods forums, part of the Tech & Modifying & General Repairs category; I currently run a lot of electronics equipment (lights, audio, etc.) and need more power. When adding a second battery ...

  1. #1
    Registered User hamz01's Avatar
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    How to add a second battery ?

    I currently run a lot of electronics equipment (lights, audio, etc.) and need more power. When adding a second battery do I just wire it in parallel with the first batter, like wiring in a capacitor? If not, how do I install a second batter?

    Thanks.
    Last edited by hamz01; 07-28-2004 at 01:51 PM.
    Brandon
    '11 WRX 5-Door, Dark Gray Metallic

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  3. #2
    He simply abides. SD_GR's Avatar
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    Use an isolator. This will maintain correct voltage and allow you to selectively charge both batteries with the alternator output.
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  4. #3
    Registered User hamz01's Avatar
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    So I do run the 2nd battery in parallel with the circuit... but I add in an isolator? What's an isolator and how do I wire it in? Also, when you say it allows me to selectively charge both batteries, does that mean the battery with the least amount of charge won't automatically recharge more than the other one?

    Lots of questions, lol. Thanks again.
    Last edited by hamz01; 07-23-2004 at 02:01 PM.
    Brandon
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  5. #4
    He simply abides. SD_GR's Avatar
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    Typically the isolator circuit sits between the alternator and the batteries. Different models have different features. You might look at RV and/or camping vehicle stores.
    WRX Info Links, Courtesy TheJ
    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
    I lied. I cheated. I bribed men to cover the crimes of other men. I am an accessory to murder. But the most damning thing of all... I think I can live with it. And if I had to do it all over again - I would. Benjamin Sisko
    DISCLAIMER: Opinions expressed are the author's alone and are inherently worthless.

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    Are you running this equipment while your car is running or while the car is off?

    If you're using it with the car running, you're just going to kill your alternator doing this. Now, your alternator will have two batteries to charge as it runs. THis will only put more strain on your alternator and not help your situation much at all. The current strain is going to still be placed on your alt, not on the extra batt.

    If you want to just use the extra battery when the car is off, fine - but it's still going to be a strain on the alt unless you use an isolator and selectively charge each battery.

    It sounds like what you shoul dbe doing here is upgrading your alternator, not adding an extra battery. Just my opinion and maybe something to consider.

  7. #6
    Registered User hamz01's Avatar
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    So everyone who's running more than one battery out there is only using it when the car's off? Is there anyway at all to add in a second battery for use when the car is running and in normal operation? I want a second battery because I am running an aftermarket sound system and many lights, with future plans to add more amplifiers, speakers, woofers, and lights. I currently am running a 1-farad capacitor. As it is, I am making excellent power, no lights dimming and excellent sustain of the bass, but I feel like a second battery would give me limitless ability for the future.
    Last edited by hamz01; 07-25-2004 at 10:26 PM.
    Brandon
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    for what you are talking about, what you DEFINITELY want to focus on is a high output alternator.

    I jsut got my sub a few weekends ago, so i'm not positive on the exact size, but i think the wrx has like a 90A alternator. Get a high output alternator like 150-200 amps and you will be good to go :-)

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    Registered User hamz01's Avatar
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    Alright cool, I will look into that. Thanks for the advice.
    Brandon
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    Registered User vtjim's Avatar
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    Just a thought... We have a Perko brand battery isolator/switch in our boat. You can switch between 2 batteries, or use both at the same time. Plus it switches to "off" and has a lock so there's no power at all.

    I'm sure it would work for a car but you'd have to find a good place to mount it.

  11. #10
    Registered User hamz01's Avatar
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    Thanks. I think it'd be weird having an isolator and having to choose which battery to be charging, I wouldn't know when to switch it or what not, and both at the same time sounds like it would strain the alternator too much, so I think I'm going to go with the alternator upgrade.
    Brandon
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  12. #11
    Registered User hamz01's Avatar
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    Where to get an upgraded alternator?

    Does anyone know where I can get a good 200A or so alternator? Are alternators car-specific?
    Last edited by hamz01; 07-26-2004 at 12:02 PM.
    Brandon
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    Re: Where to get an upgraded alternator?

    Originally posted by hamz01
    Does anyone know where I can get a good 200A or so alternator? Are alternators car-specific?
    you might want to head over to SoundDomain and ask around in the 'Electrial Explanations' forum. imtfox, a moderator over there, is usually extremely helpful. They deal mostly with very high power car installs, so alternator upgrades are a fairly common thing.

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    Hold on there!!! SD_GR gave sound advice and it was ignored. Before running to the vendor and purchasing a new alternator, you need to make sure you even need one. Most competition vehicles do not have oversized alternators, but a trunk full of batteries. I work at Soundwaves, we're currently in every R&D and Car and Driver mag, for the American Racing Avalanche and have competed and won first place finishes as IASCA and USAC. Test your total drain on the battery before you go further. If you're not exceeding the operational capacity of the alternator, no need to go bigger. You need the ability to store power, and frankly, the only thing the Suby battery is good for is a acidic doorstop or paperweight. Try an optima yellow top battery. You will have to extend the positive end of your wire harness under the hood to hook it up properly, but will work wonders for your car in general. You can pick one up for around $200. If you've got extra $$$, Rockford Fosgate makes a monster of a battery with 950 cold cranking amps. If you purchase that one, please resist the temptation to lick both terminals.
    Those fools, EVO vs. STi??? That's like comparing ....wait a minute...there's no comparison. The Suby's still working!!! The evo...well... I hope he got the extended warranty.

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    Originally posted by ej20fan
    Hold on there!!! SD_GR gave sound advice and it was ignored. Before running to the vendor and purchasing a new alternator, you need to make sure you even need one. Most competition vehicles do not have oversized alternators, but a trunk full of batteries. I work at Soundwaves, we're currently in every R&D and Car and Driver mag, for the American Racing Avalanche and have competed and won first place finishes as IASCA and USAC. Test your total drain on the battery before you go further. If you're not exceeding the operational capacity of the alternator, no need to go bigger. You need the ability to store power, and frankly, the only thing the Suby battery is good for is a acidic doorstop or paperweight. Try an optima yellow top battery. You will have to extend the positive end of your wire harness under the hood to hook it up properly, but will work wonders for your car in general. You can pick one up for around $200. If you've got extra $$$, Rockford Fosgate makes a monster of a battery with 950 cold cranking amps. If you purchase that one, please resist the temptation to lick both terminals.
    the electrical system of a competition vehicle is quite different from that of a daily driver... try charging a trunk full of batteries on a stock alternator.

    Although I do agree with you on getting the charging system tested.

  16. #15
    Registered User hamz01's Avatar
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    How can I test the total drain of my battery, and then how do I find out whether or not it exceeds the operational capacity of my alternator?
    Brandon
    '11 WRX 5-Door, Dark Gray Metallic

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