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  1. #1
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    Battery Cable Size

    I Have an XLS 22RBE.
    It has the stock 100 A/H battery and stock cables. The cables look a little small as it is.
    I would like to add a second 100 A/H battery.
    Do I need to get thicker cables, and if so, what gauge?
    Has anybody else done this?
    Thanks in advance.

  2. #2
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    4ga seems to be a common size. Battery cables for diesels may be larger because of the starting amp draw.
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    [QUOTE=BobLandry;394055]4ga seems to be a common size. Battery cables for diesels may be larger because of the starting amp draw.[/QUOTE
    Thanks for the quick response Bob.
    My rig is a trailer, not a diesel motorhome.
    I am interested in hearing from someone with a rig the same or similar to mine. These cables go to the power center, not to an engine.
    Thanks

  4. #4
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    The cables are designed for the draw, not the capacity of the batteries. You should not need to change though in my 2020 2500rl I think they were a bit small for the distance (6awg I think) so had more voltage loss than I liked

    Cheers

  5. #5
    Site Sponsor Jerryr's Avatar
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    I used 4awg cables to connect a new battery cut off switch. I believe the original cables are 6awg. These should be fine to connect a second battery. https://www.amazon.com/dp/B07L45RLY2/
    Attached Thumbnails Attached Thumbnails 5B35C314-91A8-4D27-9C97-148994AB5CF7.jpg  
    Last edited by Jerryr; 09-17-2021 at 11:08 PM.
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  6. #6
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    Quote Originally Posted by rmcrowe View Post
    The cables are designed for the draw, not the capaClick image for larger version. 

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ID:	36749batteries. You should not need to change though in my 2020 2500rl I think they were a bit small for the distance (6awg I think) so had more voltage loss than I liked

    Cheers
    I assume that increasing the capacity of the battery bank may require bigger cables, to avoid voltage drop, overheating, etc.
    The distance from the battery box to the power center appears to be about 5 feet.
    Here is a chart I copied from the internet:Click image for larger version. 

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    It looks like from the chart at 200 A/H and 5 feet I would need 2AWG.
    Is this correct, or am I missing something.

  7. #7
    Site Sponsor sande005's Avatar
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    That only matters if you will be increasing the number of amps you will use at one time. Adding 12v space heaters?? A big inverter to give you 120v?
    If the rest of the trailer remains stock, then it can't pull any more amps, no matter how many batteries you add. Those added batteries give you longer you can run, but can't increase the max amps going through the cables. You can only do that by adding more 12v things that use power to the trailer. Only then would beefier cables need to be considered.

    One thing to consider, though, is the converter that also charges the batteries when plugged in to shore power. It will now have to charge double what it did if they both are low. Which means (VERY imprecisely) up to double the time to get to a full charge.
    In my old some-other-brand that meant sometimes blowing an in-line fuse when the converter was trying to supply max charge for a long time. I cheated and put in a self resetting in-line breaker, that would allow charging to restart when things cooled down. If I still had it, I would have done more homework to look at replacing the converter, and perhaps increase wiring back to the batteries for charging. But it was totaled before I had time to fuss about that! In my current 2670MK, with 2 6 volts, since the capacity is double, charging does take longer. But no issues with blowing fuses/breakers.
    Last edited by sande005; 09-18-2021 at 05:49 PM.
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  8. #8
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    Quote Originally Posted by sande005 View Post
    That only matters if you will be increasing the number of amps you will use at one time. Adding 12v space heaters?? A big inverter to give you 120v?
    If the rest of the trailer remains stock, then it can't pull any more amps, no matter how many batteries you add. Those added batteries give you longer you can run, but can't increase the max amps going through the cables. You can only do that by adding more 12v things that use power to the trailer. Only then would beefier cables need to be considered.

    One thing to consider, though, is the converter that also charges the batteries when plugged in to shore power. It will now have to charge double what it did if they both are low. Which means (VERY imprecisely) up to double the time to get to a full charge.
    In my old some-other-brand that meant sometimes blowing an in-line fuse when the converter was trying to supply max charge for a long time. I cheated and put in a self resetting in-line breaker, that would allow charging to restart when things cooled down. If I still had it, I would have done more homework to look at replacing the converter, and perhaps increase wiring back to the batteries for charging. But it was totaled before I had time to fuss about that! In my current 2670MK, with 2 6 volts, since the capacity is double, charging does take longer. But no issues with blowing fuses/breakers.
    Thanks so much for your answer.
    My trailer is mostly stock, so you are correct that I haven't added any demand. Also, we don't intend to use anything like TV's, etc. which require an inverter and would greatly increase demand. The only "extra" is a small fan in the bedroom. I may add a fantastic fan at some point. I am also considering upgrading the existing WFCO unit with a PD. Many people complain that the stock WFCO doesn't charge at 14.4 volts, or doesn't charge at that level long enough. Some claim that this may be a result of the stock wiring being too small of gauge. I have seen recommendations of using 4 gauge between the batteries and the charger. I believe the stock wiring is at most 6 gauge.
    What you describe is what I'm trying to do: increase battery capacity for dry camping. Also, I don't want to have to run a generator forever to re-charge.

  9. #9
    Site Sponsor sande005's Avatar
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    Take a look at the chart you posted. I'm not all that knowledgeable about the specifics, but the Internet tells me one should not use a charge current greater than 25% of the total battery capacity. So 100 amps = 25 amp charge max. At 4-7 ft, the recommended wire is 10 ga. 4 ga. would be way overkill. 6ga. is fine for runs up to 10 ft, at 50 amp. (all lengths to be "round trip").
    In my boat, for example, I have two 12v batteries for the trolling motor, to give 24 v. But the charger is a "two bank" with two separate lines, each charging one battery. Each lead supplies 10 amp., but if one battery needs less than the other, it shifts the capacity to the low side - ie 20 amps max. I have no idea if there is something like that for RV use, but it would be nice if there was...
    Imagine 2670MK

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  10. #10
    New Member Stainedrug's Avatar
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    https://battlebornbatteries.com/battery-cable-size/

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