Another battery cable under the hood?

[Matt Millegan]

Found another battery cable under the hood near the engine battery.  I don't have room for another battery and I can't find the negative cable to match. Anyone know what this is for?

Check out my attachment.

[Lakota Wolf]

Do you by chance have a small compartment near your back door in the step up into the rv? My Dodge class C  in my pictures had a compartment for extra cabin battery. The Batt cable ran all the way underside from back to front, and neg cable went to frame under the small compartment in the door step.

[Matt Millegan]

I actually have 2 cabin batteries mounted in boxes on either side of the toolbox.  I am guessing that was done by the previous owner(s).  

Both of my cabin batteries need to be replaced due to weather and time.  The van battery holds a charge but for only a few days, then it goes dead.  It will also be replaced.

[Lakota Wolf]

Batteries usualy last 5 yrs,, and make sure you have a battery isolator if your charging the cabin batteries off the vehicle alternater..Walmart has resonably priced deep cycle marine batteries, and add the extended warrantee and if they go bad, any walmart will honor the warrantee.

[Matt Millegan]

I figured as much.  I can't tell exactly how old the cabin batteries are but, I can say they have seen better days.

With the cabin plugged into electric, the van battery should trickle charge given i have the switches in correct position..right?

[Richard W. Cobbs]

If you have a battery charger as part of your converter, it will send a charge to the house battery.  You need to check which battery is being charged!  Also, many of the older converter/chargers will overcharge the battery and boil out the water.  You should monitor this.  As regards the extra battery cable; the one in my RV was for starting power to the generator.

[Lakota Wolf]

I was just reading on the subject of extra batteries etc, And Richard brings up and excellent fact,, power line to Gen set. Onans do need some ooomph to crank there starters,

[Matt Millegan]

Ok, good stuff. I will trace the cable back. I'm still not finding a ground to go with that extra positive cable so, I assume it connects to van battery. Speaking of Onan, my gen cranked but acts like it's not getting fuel. Could this disconnected cable be the reason?

[Richard W. Cobbs]

If the gen cranks, then there is apparently a battery connected to it.  As to the fuel, the pickup tube for the fuel to the gen is usually kept raised up from the bottom of the fuel tank so you don't get stranded if you run the gen too long.

[John "T" Nordhoff]

  For those of you who do serious long term dry camping like we do (I have four 6 volt Golf Cart batteries in series/paralell for 12 VDC and 460 Amp Hrs of battery energy storage) , I guess you understand the so called RV/Marine batteries are semi or quasi deep cycle as compared to golf cart batteries (Trojan etc) that are true deep cycle designed with thicker plates and more life cycles and deeper discharges. Sure the RV/marine will get you by and work, but they arent designed for such low discharges and as many cycles like true deep cycle golf cart batteries are. Of course, if 6 volt, you need two in series for the 12 VDC RV requirement

 

 Many of the older generation Converter/Chargers are NOT high quality precise regulated chargers, they put out a fairly constant voltage to power up 12 VDC lights and fans and water pumps etc., and sure as a consequence, they will charge a 12 VDC coach battery, but if left plugged in for extended periods they can overcharge and boil over and ruin a battery SO KEEP AN EYE ON ELECTROLYTE LEVELS if youre plugged in for days at a time.    

 

 An extra cable can be for perhaps an Onan etc generator,,,,,,,,or for the Coach battery which, in many RV's, is also for the Generator starting. If none of the RV lights or fans or water pumps work UNLESS youre plugged into shore power (converter charge is working), you must not have a coach battery. If you hook an extra battery to that extra cable and frame ground then RV lights work even if not plugged in and the genny will crank, it must be for the coach battery

 

 Many older RV's have a relay/solenoid so that when the ign key is turned on it closes and connects the coach and engine batterys together so both are charged while driving but seperate and isolated when youre setting and engine is off.

 

 John T