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Thread: Anyone have dual batteries in your vehicle

  1. #1
    Flashaholic
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    Default Anyone have dual batteries in your vehicle

    I have heard of larger trucks and commercial vehicles having dual 12V lead acid batteries, and was wondering if anyone here knows anything about the equipment required. I am interested in dual batteries for several reasons;

    -no more jump starts necessary
    -more power for high load applications (aux lights/equipment, jumping other people's cars)
    -24V available for construction equipment accessories


    My biggest concern is how to wire the batteries to the alternator and the electrical system of the vehicle. The simplest solution would be to wire both batteries through a selector switch and then to the original battery terminals. I would just have to remember to switch the battery I use from time to time to keep both of them charged. Is there a way that I can wire both batteries so that they will both charge off of the alternator and run the vehicle's electrical system together, and possibly also have them in series for 24V power?

    Any thoughts/ideas would be appreciated
    thanks

  2. #2
    Flashaholic* Jumpmaster's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    The military M1009 (and M1008, etc.) uses dual batteries for 24v...I know that for that application at least, you'd need a different type glow-plug controller and an additional alternator...it's been a while and I don't recall what else is involved, but it sounded pretty complicated and like a project I didn't want to do on mine. I have a 1009 that the previous owner converted from a 6.2L to a 6.5L TD...it still has two batts, but wired in parallel for 12v.

    I have the military radios installed...funny thing is the mil radios (the amplifier/mount) needs 24v -- but the radios need 12v...if I recall correctly, even the audio amp only needs 12v...I need to figure out how to bypass that circuit in the mount to feed 12v straight to the amp...(there's actually three components - MT-1029 mount, AM-2060 audio amplifier, and the radio itself)...If there are any old-school 25Q's reading, please help me out on that...I'm a 25C, but we didn't learn about these things...we're not "authorized" to perform such modifications...

    JM-99

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    Flashaholic* snakebite's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    i run 2 deep cycles in paralell in a 85 olds wagon.
    the diesel version needs 2 batts so the tray is aready there.
    i can run them down to 10.5v with all the ham gear and it will still start.
    as for 24v its more work than its worth.run 2 batts and an isolator and use an inverter.

    i am always looking for old radios and tv sets.tube stuff.ham gear.i repair all the above.
    email me for more info. SPAMMERS WILL BE PUNISHED!

  4. #4
    Flashaholic
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    Default Re: Anyone have dual batteries in your vehicle

    I don't think you will want to try to wire them in series because your car charging system will only charge to about 14 Volts. That said, the marine and car audio world does this dual battery thing all the time. You can buy a battery isolator ( basically a diode system) to allow your alternator to charge both batteries at the same time, and they can get discharged (wired) seperately so you pull from whichever battery you are wired to.

    Do a Google search on 'battery isolator' and you'll get lots of products.

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  5. #5
    Flashaholic* KC2IXE's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    Quote Originally Posted by bexteck
    ...snip... I am interested in dual batteries for several reasons;

    -no more jump starts necessary
    -more power for high load applications (aux lights/equipment, jumping other people's cars)
    -24V available for construction equipment accessories

    ...snip...
    wiring up for 24 volts would require changing almost everything in your truck

    Now, as for dual 12 volt systems - I had one on my old truck, and will do it eventually on this truck - the reason I do it is I have a lot of ham radio gear that I like to run for HOURS with the truck off

    You can parallel 2 starting batteries for more cranking amps, but this is sort of a waste - what most people really want, if they want to run "accessories" is to have the starting battery, and a deep discharge battery for the accessories - you use a dual battery electronics box to set them up, and move the accessories to the 2nd battery - when the truck is charging, it charges BOTH

    The BIG problem is that most of them have some voltage drop across the box, so your batteries never really fully charge - it can also be done with a continuos duty relay of a fairly high current rating (say, 100 amps) that is hooked to a circuit that is ON when the truck is running, but OFF when cranking or not running - no voltage drop. You then do NOT have to worry about voltage drop - the disadvantage is that it's much harder to parallel them if your prime battery goes dead

  6. #6
    Flashaholic* Pydpiper's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    There are kits available at auto part stores to use two batteries, simple to install and safe to use. It is common to do this for many reasons, but to answer your original question, yes, it can be done.
    trying to get 24 volts is possible too, but you don't have a use for that..
    Try googling "wrangler dual battery kit" They are a reputable company that provides what you need.
    Just one more light and my collection is complete! Ok, maybe two..

  7. #7
    Flashaholic
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    Default Re: Anyone have dual batteries in your vehicle

    Quote Originally Posted by KC2IXE
    wiring up for 24 volts would require changing almost everything in your truck

    I didn't mean running the whole truck on 24V. I just wanted it available for individual accessories like the huge amber rotating lights you see on construction equipment. The rest of the truck would remain 12V.

    The aspect of dual batteries that I am looking for most is redundancy. If for some reason one of them fails, I will still have one good one to use. The whole 24V idea is just an afterthought.

    I have heard that boats very commonly have 2 batteries. When I get a chance I will have to look into the method of wiring they suggest. I am starting to think that just wiring them both with a selector switch between the main battery terminals may be the most feasable option.

  8. #8

    Default Re: Anyone have dual batteries in your vehicle

    Dual battery setups are fairly common on 4x4 rigs. They are desirable for redundancy and primarily so that tons of current is available to power a winch. Main concerns are usually fitting it all in, charging both batteries properly, and keeping the batterys from draining each other.

    These are pretty good links on how and why to do it:
    http://www.4crawler.com/4x4/CheapTri...atteries.shtml
    http://www.off-road.com/jeep/swb/art...lectrical2.htm
    http://www.off-road.com/chevy/reviews/hellroaring/

    Geoff

  9. #9
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    Default Re: Anyone have dual batteries in your vehicle

    In my old car I can a relay or contactor that closed when the ignition was on, but could also be manually switched on or off. I had the regular 80AH 800cca front battery and 2 120ah 12v marine batteries in the trunk power inverters and extra lights

    In the marine world the smaller boats use a similar setup a "starting" battery and then "house" battery or batteries. The selector switch often has off / 1 / both / 2 and back to off. In this case except in off you never disconnect a battery from the engine, doing so can cause bad things to happen. The only time you go to "off" is if your gone for a while and want to make sure nothing is left on and no one can steel the boat without knowing where the battery switch is and some even have a key to lock them in the off position.

    On larger boats the starting battery is always connected to the engine or engines, often a starting battery for each one. Then an auto contactor that once the engines are running connected the house bank, often very large like 500AH or so and charge automatically. The last boat I took care of had 2 starting batteries, one for each engine, 1 small starting battery for the genset and 4 large 4D deep cycle for the house bank. If you somehow managed to run them all dead then you deserved to sit in silence Although in this case since the genset was separate you could even pull start that in a pinch and that feed 2 100 amp iota chargers that could charge any or all the other batteries and then get the big diesels started.
    Brock - Used to have some web sites

  10. #10

    Default Re: Anyone have dual batteries in your vehicle

    Very easy to do. Most full size trucks had options of having a diesel engine so you just lookup the part for the second battery tray and bolt it in.
    Ideally you should have some sort of isolator be it relay or diode. The relay will just connect both batteries in parallel so you want to have them close to the same size and age since they will both get the same charge and its possible if you have two older batteries and discharge one real low that you can still have trouble starting because the 'dead' battery drops the voltage on the main battery.
    the downside to the diode type is the .7v drop across the diodes but GM has a sense wire you can run from the alternator to the main battery to the regulator takes reading from there so it will compensate for it, downside is the charge reading is still coming from one battery.
    Really fancy and $ systems (think ambulance) have dual alternators so one can charge each battery completely independently.
    I put the diesel tray in my new truck and threw in an old battery for now but haven't finished wiring up the isolator yet.

  11. #11
    Flashaholic*
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    Default Re: Anyone have dual batteries in your vehicle

    It really is simpler than it sounds. RV's use this type of setup. This way when you are parked, and running from one battery, you don't drain the main battery for the motor. The alternator charges both, but you only drain one. The kits aren't hard to find if you search for them.

    Good luck
    "LIFE………….is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming - WOW - What A Ride!" #3475

  12. #12

    Default Re: Anyone have dual batteries in your vehicle

    Older large diesel engines use a dual battery setup. I believe they are just parallel.
    There are also battery isolators that allow you to use a second battery and drain it down/charge it up without affecting your vehicles starting battery.
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  13. #13
    Flashaholic* Unicorn's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    You won't be able to have dual batteries and be able to have some things run at 24 volts, and the rest at 12. Just run them in parallel, and you'll have plenty of amps to run the add on lights. Look at the ones used on police cars and tow trucks. The strobes use less power and are brighter and longer lasting than the halogen ones (which just use 55watt H3's).

  14. #14
    Flashaholic* BIGIRON's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    My Ford diesel camper truck has duals. I have a knife switch on the one farthest from the starter. I generally isolate it when fully charged and keep it as a back up. The dual batts are only needed for a cold start in really cold weather -- something I only see on trips north.

    I have a deep cycle batt in the camper. Instead of using an isolater, I just wired in a 10ga charging wire thru a simple push/pull auto switch. That way, when using the camper batt, I can isolate it easily. When it needs charging, I just close the switch and draw off the vehicle system. I've been careful to only charge when the crank batts are fully charged to avoid a alternator overload (not likely, buy why chance it). This also lets the 12v fridge work fairly well when travelling.

  15. #15
    Flashaholic
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    Default Re: Anyone have dual batteries in your vehicle

    Thanks for all the input, I will probably end up waiting until spring to put in one of the kits, as working on an engine when the temperature is below freezing is not a whole lot of fun.

  16. #16

    Default Re: Anyone have dual batteries in your vehicle

    The manual switches work too, I just prefer an isolator so I don't have a switch to forget about. I've thought about making a simple time delay ckt to turn on a relay a couple minutes after starting that way it doesn't connect both batteries right away.

  17. #17
    Flashaholic* Morelite's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    Quote Originally Posted by Unicorn
    You won't be able to have dual batteries and be able to have some things run at 24 volts, and the rest at 12.
    Yes, there is a way to have dual batts and run the vehicle on 12 volts with both batteries in parallel and also have a connection that is 24 volts. Our company trucks (Chevy silverado's) have dual batts and a plug-in connection for jumping the heavy equipment. I would have to look at them when I get back to work but I do know that there is two different types of battery isolators/combiners in there and lots of extra cables and a few 600+ amp diodes. That setup is not OEM it was added by one of the heavy equipment dealers (Cleaveland Brothers IIRC)
    Last edited by Morelite; 01-01-2006 at 07:35 PM.

  18. #18

    Default Re: Anyone have dual batteries in your vehicle

    I have a 96 gmc sierra that I purchased used. It came stock with two batteries. It is part of a camper/trailer package that allows you to use the second battery and will not drain down the primary. I have never used for camping, and it is always charged (ran battery down with dome light over several weeks of not being used.) I just jumped from the secondary battery. I know it charges constantly, but does not seem to drain from any truck accessories / engine system.

    You can run two batteries in parallel but I am not sure of length of lifetime problems from internal resistances between the two. Tractor trailers use bank of 6 batteries in parallel from what I have seen. The get hard use/constant charging and discharging from loads/inverters with engine off. extreme heat/cold so batteries dont last but a few years. I dont know if I would personally try running in parallel rather than with an Isolator. it probably depends on how much constant drain you have on the electrical system --if you are running huge car stereo, etc. and would probably be better in that case to use an isolator and higher amperage alternator so when you run battery down you can still jump off the secondary.

    I dont know if this helps any but just my personal experiences
    good luck

  19. #19

    Default Re: Anyone have dual batteries in your vehicle

    Our 2011 Chevrolet Tahoe has a second battery tray under the hood, and a dash switch to allow the charging system to run harder when towing to keep a trailer battery topped up.

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  20. #20
    Flashaholic* Lou Minescence's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    Bexteck, knowing what type of vehicle you have would be a help. If you have a pickup, check with a dealer about the optional battery tray that would have come with the truck if it had dual batteries as a factory option.
    You would also be able to buy the positive battery cable that connects both batteries positive terminals. then you would need a negative cable to ground the second battery. That would be the quickest way to convert. Another thought is how many amps is the alternator rated for ? You may want to upgrade it to a higher output version but it shouldn't be necessary. It will be expensive and or time consuming to add another battery. If you want to isolate the battery as others suggest, talk to an RV dealer about it.

  21. #21
    Flashaholic*
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    Default Re: Anyone have dual batteries in your vehicle

    You guys do realize you are responding to a 5 year old thread right? I would assume the OP has already made whatever changes he planned on a long time ago.
    Travis

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  22. #22
    Flashaholic* Lou Minescence's Avatar
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    Default Re: Anyone have dual batteries in your vehicle

    It may be a work in progress. OOPS !

  23. #23

    Default Re: Anyone have dual batteries in your vehicle

    I don't have dual batteries in my Accord, but I DO have a very oversized deep-discharge battery, one that in fact ever so slightly bulges the hood- but which I consider to be very good backup over the regular sized Accord battery in below zero cold start situations and general emergencies that might require the emergency flashers or other lights, and/or the radio, to stay on for an extended period.
    It is better to light up one LED than to curse the darkness.

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