Forum Discussion

altblank's avatar
altblank
Explorer
Mar 14, 2022

connect coach and house batteries?

hey all. we have a 2004 coachmen freelander 3100so with the ford e-450 super duty engine.

i recently replaced both coach and house batteries (we bought the rig 1.5yrs ago and these were simply old and wouldn't hold much charge), with new interstate 12v agms. house got a group 27 and coach got (if i remember correctly) a group 24.

now the house battery is part of a solar charging system. 2 100w panels through a 30amp pwm charge controller maintain the house battery, and this has been working like a champ for the 10 or so months this has been in place.

however, the coach battery is a different story altogether. even though nothing is running, it runs down entirely within a week or so of sitting. i suspect that the alternator is bad, but don't want to dig in and see what's going on just yet (don't have the skills *yet*).

i'd like the solar panels to charge both house and coach batteries if possible, and am considering two options:
- one, add a positive wire between both batteries (assuming they're grounded to the same setup) so any overage from the house battery trickles down to the coach battery
- two, change the momentary battery boost button to an actual toggle (and leave it on), assuming that this won't screw up the larger converter or other systems

any advise is appreciated... if i'm clear to go option one (which i prefer), is there a shorter path to connect both batteries together instead of routing an 8gauge wire between house steps and engine bay?

thank you!
  • Lwiddis's avatar
    Lwiddis
    Explorer II
    Mar 14, 2022
    Matt's right. Get it fixed right. It will never fix itself and makes your vehicle undependable.
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Mar 14, 2022
    Hey Alt,

    You really should just bite that bullet and fix it right the first time. It's an 18yo coach and someone has connected something to the chassis battery that should not be there. So, pop the hood and look for what got added first. If you don't find it, attach two wires with alligator clips to a small (like interior light size) light bulb.

    Put that in series with the main engine (aka chassis) battery and start pulling fuses and disconnecting things. Neither the keep-alive power for the ECU or the radio should light a small light bulb, but if something does, find out what it is.

    When you have that found and removed, the find a Trik-L-Start or similar to keep the chassis battery at full charge.

    Matt
  • way2roll's avatar
    way2roll
    Navigator II
    Mar 14, 2022
    altblank wrote:
    hornet28 wrote:
    You have a drain someplace. Use a battery shutoff on the coach battery


    agreed totally, there's a definite drain somewhere. but a shutoff means i'm wasting the excess solar power that's generated for free, and i'll just be that bit closer to having the engine battery work better... but not quite.

    thanks!


    You're not wasting solar, you just aren't leveraging it for charging your chassis battery (coach and house batteries are the same thing). And you shouldn't have to. And a shut off would stop the drain. You wouldn't continually run water to fill your FW tank because it had a hole in it would you? You would find the leak. Your Chassis battery (like any car or truck) gets charged by the alternator when running and if things are working as they should, should not need recharging for a reasonable amount of time. A week is unreasonable. House/coach batteries however get used while camping and thus the reason for the solar charger to keep them topped off.

    You are attempting to put a band aid on the problem. You need to find the reason for the chassis battery drain. Or at a minimum, install a shutoff to stop the drain.

    On edit - something to consider with your proposed solution of linking the House and chassis batteries together to benefit from the house battery solar charging. Whatever the draw is on your chassis battery could be strong enough to now also drain the house batteries in spite of adding them to the solar chain. The point is that you don't know what this draw is causing the chassis battery to be drained in a week. And if you don't know that, you don't know that the solar which would now be required to charge yet another battery, is enough to offset that drain. You could potentially exacerbate your problem by spreading the drain to the house batteries.
  • BFL13's avatar
    BFL13
    Explorer II
    Mar 14, 2022
    altblank wrote:
    BFL13 wrote:
    Run that from inverter on house


    thanks, but I don't have an inverter on the house battery; only a converter / charger.


    I was able to fashion a socket to socket cable using 12v plugs that goes from the house powered TV panel socket down to the engine batt powered dash socket. Tricky getting polarities right reversing end to end.

    Another way is portable solar just on the engine batt.

    Hard to parallel the batteries from inside instead of external jumper. The Ford isolator is ignition controlled. I suppose you can go through the emerg start somehow--Class C in sig doesn't have that so don't know how.

    Easier with a Chev via 7-pin where 12v is always on with engine off.
  • altblank's avatar
    altblank
    Explorer
    Mar 14, 2022
    hornet28 wrote:
    You have a drain someplace. Use a battery shutoff on the coach battery


    agreed totally, there's a definite drain somewhere. but a shutoff means i'm wasting the excess solar power that's generated for free, and i'll just be that bit closer to having the engine battery work better... but not quite.

    thanks!
  • altblank's avatar
    altblank
    Explorer
    Mar 14, 2022
    BFL13 wrote:
    Run that from inverter on house


    thanks, but I don't have an inverter on the house battery; only a converter / charger.
  • hornet28's avatar
    hornet28
    Explorer
    Mar 14, 2022
    You have a drain someplace. Use a battery shutoff on the coach battery. Here's an example
  • BFL13's avatar
    BFL13
    Explorer II
    Mar 14, 2022
    Plug a 2a maintenance charger that has a 12v plug into the dash cig lighter socket

    Run that from inverter on house Not efficient but who cares with solar
  • way2roll's avatar
    way2roll
    Navigator II
    Mar 14, 2022
    It sounds like you may want to find out what is drawing on your chassis battery that's causing it to drain like that before going through any mods. A chassis battery should not discharge completely in a week. Something is drawing it down - a light left on, the radio etc. You could (or should) install a disconnect on the chassis battery and shut it down prior to putting the RV away for any length of time. Granted an alternator could be part of the problem but it sounds like it's going dead in a week of sitting and not running in which case neither is the alternator.

    You did mention you just replaced the batteries. Did this problem occur before you replaced them?

    If you wanted to try to see if a solar charger would help, try a stand alone model for little cost before running any wires.

    Car solar charger

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