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Muddydogs's avatar
Muddydogs
Explorer
Sep 12, 2014

Extra trailer battery's

I have two batteries on the trailer but for my 2 week boon docking trip I was thinking about taking along 2 of my boat deep cycles as well. Can I leave the 2 trailer battery’s hooked up to the trailer just like they are and just wire the 2 other battery’s in parallel? I guess what I’m asking is does it matter where the trailer leads hook into the battery bank?

Here’s a pic, can I do this?

My trailer batteries are Interstate group 24 and the 2 extras are Kirkland group 27’s plus the Kirkland batteries are older but charged right up to 12.6 volts and help it for 48 hours. I am going to check the batteries tonight after they have set for 5 days and see if they have held the charge then apply a load tester and see where there at. If the Kirkland’s test out ok will adding them have any negative impact overall? I have read that you shouldn’t mix sizes or new and old batteries but nothing as to why not. Since I am only doing this for a 2 week time frame will it reduce the life of the 2 trailer batteries?

12 Replies

  • In an nutshell, yes you can cheat and do that. Because it is short term and you don't plan on withdrawing or adding large amounts of amperage. However what CT Wanderer posted has a lot of merit. Pianotuna may chime in and post his balanced batteries wiring diagram.

    But in order to get your money's worth out of the modification it is best to make certain all terminals and battery posts gleam when making the connections.

    CHEATER'S TIP

    Use jumper cables

    Connect the positive jumper cable from the first battery positive to the last battery positive.

    Connect the negative jumper cable from the first battery negative to the last battery positive.

    It may not end up looking pretty, but I imagine your goal is to do the best you can with what you've got. No moving of the original battery connection wires. Easy and effective. This will do it, even if you should have a high draw inverter and use it.

    Have a great vacation and give a smug little smile at the extra battery capacity.
  • If I was going to do this I would move the Neg cable to the far end of your added batteries.

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