Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 12, 2025 ...

Please look at my start battery bay...it may be wired incorrectly.

August 26, 2022, 01:55:24 pm

I am getting ready to replace the 2 older Interstate batteries in our 1997 U270 in anticipation of a couple weeks boodocking at the Texas coast in mid September (the 8D house batts were replaced 2 years ago and are doing fine).  These 2 Interstate batteries were installed well before we bought the coach 6 years ago and need boost to start if the 24v Battery Tender is not plugged in....however they have always easily started the 8.3 mechanical control Cummins engine when the Battery Tender has been plugged in to 120v (99% of the time).

Please look at the very dirty setup that has served us well for the past 6 years.  I think the batteries are correctly wired in parallel which means they feed the starter motor 12 volts (OEM setup).  HOWEVER.....the 24v Battery Tender is wired in series in the pic!  It is a 24v 2 Amp battery maintainer and indicates 24v on the housing with a green light.  I think when I put this in 6 years ago I wired it wrong thinking the entire coach was 24v but realize now on closer inspection that the starting circuit is actually 12v.  I am not sure why it even works.  I plan on fixing this when I install new batteries this weekend with a new Battery Tender that is 12v 2-6 amp and will wire it to the outboard battery's + / - post

Please someone confirm that I am on the right track and that the starting circuit and starter motor are indeed 12v (and not 24v) and that the connection of a new 12v Battery Tender is going to work.  It is a simple setup that I got wrong long ago...good news is the coach has been very reliable and other than the need for a boost switch startup if the Tender is unplugged for a couple days has been trouble free with no electrical gremlins.  I am only replacing the batteries as a precaution as I know they must be near the end due to age and the Battery Tender may not have power for a couple days boondocking.  Any advice appreciated!

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Re: Please look at my start battery bay...it may be wired incorrectly.

Reply #1 – August 26, 2022, 02:11:00 pm

Looks like the batteries are wired for 12 volts,here's what I would do,take all those connections in the picture off and clean them and the batteries,get a 12 volt battery minder brand charger that can desulphate and charge 12 volt batteries,get a volt meter and when the engine is running make sure you have good charging voltage,about 13.8 volts.The battery minder will tell you if you have a weak battery,you may not need new batteries.While your at it,clean the terminals on the starter and the alternator and the battery isolator,do that and let us know what happens.

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Re: Please look at my start battery bay...it may be wired incorrectly.

Reply #2 – August 26, 2022, 02:29:24 pm

Wired fine . The tender being 24 volt wil try to cook the batts tho. 

 You should check the water in the batts. Good chance that it's missing some and they may live a little more.
      Thanks for posting the pic. I feel embarrassed posting my battery /wiring pics, less so now.   

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Re: Please look at my start battery bay...it may be wired incorrectly.

Reply #3 – August 26, 2022, 03:03:09 pm

Everything is wired in parallel. Yep as you know in need of being cleaned and protected from being exposed to the air. Grease or spray. Lead acid batteries will require maintenance so if the cables are installed to allow access to caps it will make servicing them easier. I have learned from Lynn S. That if cables are used like we do ground wires and Positive should be on opposite batteries to enable equal charging. Not needed if your using battery busses. I also like to make the ground primary disconnect lug easy to access in case of a emergency. Definitely need to get the proper voltage battery tender. Going one step further I even checked the water level in my Napa group 31 maintenance free  batteries and found several near the low limit of exposing the plates. I know its more work now but will enable checking the water levels and possibly make the batteries live longer.
Scott

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Re: Please look at my start battery bay...it may be wired incorrectly.

Reply #4 – August 26, 2022, 05:01:01 pm

The one change I would make is to SPAN the battery bank with your output wires.  The positive wires go to the positive post on battery 1 and the negative wire goes to the negative post on battery 2.  I wire a 12 vdc Battery Tender the same way.

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Re: Please look at my start battery bay...it may be wired incorrectly.

Reply #5 – August 26, 2022, 08:03:07 pm

Actually, the battery charger is NOT wired in series.  Note that, even though the charge appears to be connected to the negative of one battery and the positive of the other, both battery negatives and positives are tied together so, even though it looks that way, it is really connected in parallel...attempting to put 24 volts on to your 12 volt batteries.

As others have indicated, you need to
    1. Get a 12 volt charger and connect it in the same way as the current one.
    2. Disconnect all the cable and clean them and apply anti-corrosion spray or grease.
    3. Reconnect the cables with the aim to have access to the caps without having to remove the cables.  I would take the connection that is currently on the inside of the rear battery, positive terminal and, if you can, rotate it so that the flat side of the connector on the end of the cable faces to the right and place it butt-to-butt with the other cable that is also connected to that clamp.  That would putt both cables on the outside of the terminal clamp and give you better access to the battery cell caps.
Then, rotate the clamps in the left (both front and rear batteries) counterclockwise and the ones on the right clockwise to increase the amount of slack in the interconnecting cables and route them a bit more away from the battery caps...giving you better access to the front battery caps.
As for the current batteries, I agree that you should check/fill them (distilled water only) and they may come back but they may also be done at this point.

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Re: Please look at my start battery bay...it may be wired incorrectly.

Reply #6 – August 27, 2022, 07:37:34 am

FWIW since discussion of the 2A 24V battery tender is an academic discussion at this point.
And IF that 24V battery tender has not long since gone to sing in the choir invisible.
That battery tender, if current limited, would have had it's 24V output swamped by the demands of those batteries, to put it another way, those batteries never saw 24V from that battery tender.

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