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Dual Bat Q's

Discussion in 'The Garage' started by Hossbaby50, Jul 13, 2004.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    Dual Bat Q\'s

    I have a question on running dual batteries. I want to run them off a Perko switch or something similar.

    Can you run two different batteries? I want to add a second Optima Redtop or a Marine deep cycle battery as the second battery. Would running one Redtop and one Marine battery hurt anything? I want to run my winch off the Marine battery since I don't have/can't afford a high output alternator yet.

    If you ran a Perko switch and were running off 1&2 would the alternator trip out because of the two different batteries? I would only really use the second battery when I was winching or when I was on a night run with the lights on at slow speeds.

    Harley
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: Dual Bat Q\'s

    It'll be fine. The factory has been wiring them together without a switch or isolator for a long time.
     
  3. hardcore71

    hardcore71 Registered Member

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    Re: Dual Bat Q\'s

    Actually the factory (GM anyway) uses an isolator. If you just wire 2 batteries together and let the truck sit for any length of time you will have 2 dead batteries. This is known as dualing battery sydrome. One batt will allways have a slightly lower charge than the other. The one w/ the higher charge will try to "charge" the lower. Voltage drop through the wires and connections will result in less voltage reaching the second bat than left the first. As a result the original "higher charge bat" now has a lower charge than the "lower Charge" bat. This back and forth will continue until both are dead. Kind of confusing but true.
     
  4. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: Dual Bat Q\'s

    [ QUOTE ]
    Actually the factory (GM anyway) uses an isolator. If you just wire 2 batteries together and let the truck sit for any length of time you will have 2 dead batteries. This is known as dualing battery sydrome.

    [/ QUOTE ]

    Maybe in theory.

    I've left mine hooked up for two weeks at a time without starting my truck and never had issues.

    I usually unhook them anyway but if you have two similar batteries they will not kill each other.

    The factory does not use an isolator, they're wired together.
     
  5. backcountry

    backcountry 1/2 ton status

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  6. Mastiff

    Mastiff 1/2 ton status Premium Member

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    Re: Dual Bat Q\'s

    [ QUOTE ]
    Actually the factory (GM anyway) uses an isolator. If you just wire 2 batteries together and let the truck sit for any length of time you will have 2 dead batteries. This is known as dualing battery sydrome. One batt will allways have a slightly lower charge than the other. The one w/ the higher charge will try to "charge" the lower. Voltage drop through the wires and connections will result in less voltage reaching the second bat than left the first. As a result the original "higher charge bat" now has a lower charge than the "lower Charge" bat. This back and forth will continue until both are dead. Kind of confusing but true.

    [/ QUOTE ]

    Don't diesels always have two batteries just wired together in parallel? By your logic, most electronic devices that use multiple batteries would kill the batteries in short order, even when off?
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: Dual Bat Q\'s

    [ QUOTE ]
    [ QUOTE ]
    Actually the factory (GM anyway) uses an isolator. If you just wire 2 batteries together and let the truck sit for any length of time you will have 2 dead batteries. This is known as dualing battery sydrome. One batt will allways have a slightly lower charge than the other. The one w/ the higher charge will try to "charge" the lower. Voltage drop through the wires and connections will result in less voltage reaching the second bat than left the first. As a result the original "higher charge bat" now has a lower charge than the "lower Charge" bat. This back and forth will continue until both are dead. Kind of confusing but true.

    [/ QUOTE ]

    Don't diesels always have two batteries just wired together in parallel? By your logic, most electronic devices that use multiple batteries would kill the batteries in short order, even when off?

    [/ QUOTE ]

    1. Yup I said this twice already.

    2. His logic isn't flawed but just unrealistic if you've got two good batteries.
     
  8. az-k5

    az-k5 1/2 ton status

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    Re: Dual Bat Q\'s

    That can happen to batteries. It has to be a closed loop for it to happen though that is why a flashlight won't do it. If you have no dead shorts it shouldn't charge/discharge.
     
  9. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Re: Dual Bat Q\'s

    Almost all of our semi trucks have 4 batteries wired in paralell. When the batteries go dead you just have to get the charger and load tester out and find the bad one. If I ever go to dual batteries i will just wire them together, doesn't bother me.
     
  10. Xtreme Off-Road

    Xtreme Off-Road Registered Member

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    Re: Dual Bat Q\'s

    It is O.K. to hard wire 2 batteries together as long as they are the same. The problem with doing it with 2 different batteries, even if they have the same ratings, is that they may have a different internal resistance. This will cause the alternator to charge the lower resistance battery for a longer time and possibly causing an over-charge in the other battery. Over a periode of time this will damage the battery.
    That is why factories can do it, but they always use identical batteries. Even in big trucks.
     
  11. MarcS

    MarcS 1/2 ton status

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    Re: Dual Bat Q\'s

    Each battery will draw the current it needs to charge from the alt. It will be fine. Isolaters cause voltage drops, and battery combiners just automatically connect and disconnect them together (Keeps both charged also). The battery switch is the easiest and cheapest way to do this. You don't have to run the switch on both unless you want to charge both. Leave the second battery isolated from all accessories, alternate from 1 to 2 daily and they will both be charged and the isolated battery will always be ready if the other one dies. Use Both when winching. /forums/images/graemlins/thumb.gif
     

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