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Tow Rigs, Trailers, and Other Tech Discussion Have a Tech question NOT related to an XJ or MJ? Have Tow Rig or Trailer questions? This is the place to get help.

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  #1  
Old July 25th, 2004, 19:42
MACH90XJ's Avatar
MACH90XJ MACH90XJ is offline
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Location: Oregon
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Whats killing my Battery ?? dual battery system

My old 77 chev van is usually trouble free but it seems to be slowly killing my primary starting battery,I have dual battery setup, factory type setup its a camper type van.Charging seems to be taking place as the aux. batt reads 14.3v,I cant get the primary bat to take a charge this time.I have put new batts in the past but I just dont use this van enough to watch the voltage drain,I put maybe 700 miles a year on it,last year I used it in october and never started it til May of this year. I usually just jump it from the aux batt and drive for a while then it seems to charge with a good battery,but when it sits for awhile primary bat is dead and aux is fine at 12v .Now it wont take a jump unless I have the aux hooked up ?Hell I dont know what up with this thing ,probably right in front of my nose.

I have done some basic multimeter testing but Im missing or doing these test wrong.Thats where you guys come in,What are the testing procedures for a dual batt setup to check for a draing batt problem.I was told something in the alternator could be draining it also? It has an isolater type thing between the 2 batts,I assume thats what it is. Electrical is definately not my specialty either is a dual batt setup.

Any help would be appreciated as the only time I really use this van is up in the mountains along ways from home or other people.
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Old July 25th, 2004, 21:31
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8Mud 8Mud is offline
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Re: Whats killing my Battery ?? dual battery system

The easiest way to test for a slow drain, is to unhook the POS. cable and measure voltage, between the cable and the POS lug, on a full battery. With all the doors closed and the ignition off, the drain should be close to Zero. If you find a drain, have to check one sub system at a time, till you find it. You can (if you have a digitial meter) try some of the more sensitive scales, to check for voltage to ground through moisture. You can loose juice through moisture, but very slowly. If checking a voltage leak through moisture, with an ohm meter, you often need more than 6 volts (9 volts is better) to measure the loss, with an ohm meter. An ohm meter with a 1 1/2 volt battery isnīt hardly going to register.
Some things, often overlooked, are a dirty battery, acid crsytals mix in with the dirt and will drain your battery. If your battery is the type, where you add water. Look in the holes with a flashlight and check what shape your cells are in. Are they swollen or split, covered in a crust? A quick and dirty test for a battery, is with a fully charged battery, start the truck with a voltmeter hooked across the battery poles, if it goes much below 9 volts (during cranking), the battery is questionable, time for a trip to Auto Zone for a battery test.
Repeatadly, fully draining a battery and then rechargeing, will slowly kill it.
I bought an electronic battery charger, got a long extension cord and a lamp timer. I leave a very small bulb burning (pair of aligator clips to an always hot wire, to ground) and set the lamp timer to charge the battery twice a day, for half an hour or so. Campers always ready to go in the spring.
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Old July 26th, 2004, 22:24
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MACH90XJ MACH90XJ is offline
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Re: Whats killing my Battery ?? dual battery system

Thanks Ill try that when I get a new battery,This battery just wont take a charge anymore.It is not serviceable,no add water type(Interstate).Auxillary batt is deep cycle,so it can handle the drain down if need be.

Maybe you have some knowledge of this isolater, is it testable with a voltmeter? My guess is it is working because my auxilary batt is not draining down one bit or could it be actually draining primary? I'm not the type to let some kid at Autozone guess what parts I need,I would like to get my facts straight and tell them what I need.I'm not saying all parts guys dont know anything but its rare to find one that doesnt have to rely on that little computer.Just a little rant about parts stores and mechanic shops in general,Im done.

Appreciate your time,Thanks Mike.

Loss through moisture ?meaning water on battery or cable connections?Water on ground cable?Not sure what your talking about here.

Last edited by MACH90XJ; July 26th, 2004 at 22:31.
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Old July 27th, 2004, 16:26
Ivan Aby Ivan Aby is offline
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Re: Whats killing my Battery ?? dual battery system

If your battery is sitting below 13v the chemistry changes to producing sulfation. Sulfation is the primary way batteries are killed in standing (unused) situations. You might have a very slight parasidic draw in the van (clocks, computers etc) but driving a vehicle less than 700 miles a year is a reciepe for battery failure.

Try this: When back from your trip, charge up your batteries to 13.6v and pull a cable. They should be good for six months at a time without issue.

Also, trying going to a deeper cycling battery for your starting one. It has helped in a friends CJ that he rarely drives.

No matter what, the sulfation issue (battery undercharged and then sitting for weeks) will be the major issue you are experiencing. Quick way to tell without popping caps; look at the side of the battery. Is it chubby? If your battery looks like it just got done eating Thanksgiving dinner then it is sulfated.

One last thing. If your vehicle does sit for extended periods, blast charge your battery. Put it on a very hot charge (50 amps) for an hour or until the battery is hot to the touch. This helps eliminate sulfation build up on the plates and reverses some of the degredation process. Don't worry about "buckling" the plates, this myth is a complete falacy. Nor will the battery blow up unless you have a spark (byproduct of charging a lead/acid battery is hydrogen....don't smoke around 'em).

I hope it helps,
GC
President
Force Batteries

EDIT - if your primary is dead (9v or less) and your aux is discharged at 12v then something is amiss. Parasidic drain or old batteries that won't hold shelf life. Most good batteries can hold six months without a charge without issue. However, 12v is a battery that is very discharged, which tells me something else is at work here. What is the date code stamped into the top of the battery (number and letter)?

Last edited by Ivan Aby; July 27th, 2004 at 16:29.
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