Help diagnosing a battery

JDaPP

Adventurer
Have a 2012 Jeep Wrangler Rubicon with the Genesis dual battery system. I have two standard Walmart Everstart batteries that are about 2 and 1/2 years old (I know I should be getting something like the optima battery but I won the Genesis system and at the time I just couldn't afford it/I wasn't using it that often).

Over the last six months every so often the main battery will just not allow the vehicle to crank. Sometimes it is after sitting all night, sometimes it is after an hour. As soon as you put it on the charger it goes right to 12.7 volts/indicates good. I took it into Walmart they tested and said it was good. Usually I swap the batteries and then it'll work for a little while and then they'll do the same thing.

Any thoughts on what might be going on? Is there something wrong with the isolator? Both batteries charge, both batteries hold a charge, I've never depleted them so far down that they were completely dead and as soon as I apply a charger of any type they are at full voltage, in fact every time I try to test them I've never seen them below 12v. Is it the type of batteries?
 

luthj

Engineer In Residence
Please describe the event in more detail. You turn the key, and what? Clicking, but no rotation? No clicking or activity at all? Slow crank, and then nothing? Detail is important.

There are many parts involved with starting the engine. The battery, wiring, ignition switch, starter motor and solenoid, ground straps, etc. Any one of them could cause a start failure.

What is the resting voltage of the battery? This is after sitting at least 6 hours with no charger. 12 hours is better.

I am assuming walmart did a load test? If so, what was the CCA the test reported?
 

JDaPP

Adventurer
no clicking, and no turn over. I removed all accessories that were attached to main and aux with no noticable affect. The isolator has a button that is supposed to allow the two batteries to connect for a dead battery start. When I press it nothing happens. After I change the battery order around then the button will work and connect them.

Walmart test was pretty useless as it just said battery tested good with no other information. Will get the resting charge and post it tomorrow.

What is weird to me is if I move the batteries around then everything works fine for a while.

Appreciate the help.
 

shade

Well-known member
What is the resting voltage of the battery? This is after sitting at least 6 hours with no charger. 12 hours is better.
^ That, for both individually.

If the batteries are charged, from the behaviour before & after you move them around (no power, then everything works), it could be a bad connection. Do the batteries share a ground connection?
 

jonyjoe101

Adventurer
when I had a similar problem I was able to track it down to a sidepost bolt that was too short, this didnt allow the sidepost to tightend all the way down. When this happens the battery isn't fully charged, the alternator produces enough current to run everything while engine is running. Since both batteries are connected together they would both be undercharged.

On mine it was a sidepost but it can also be a loose connection anywhere that the battery terminal wires go attached too. But also check that the alternator is putting out enough output to charge the battery.

Once the battery is chronically undercharge, they loose capacity, if as soon as you put a charger it climbs rapidly to full thats a sign it lost capacity. It will still work if you fully charge them everytime.
 

shade

Well-known member
The isolator has a button that is supposed to allow the two batteries to connect for a dead battery start. When I press it nothing happens. After I change the battery order around then the button will work and connect them.
This is the part that makes me think you have a bad connection that you're disturbing in the process of swapping the batteries.

If no charge has been added to the batteries and they're at too low of state of charge to start the engine or even power a light, but they suddenly deliver enough power for both after moving things around, I think you have an intermittent connection.
 

JDaPP

Adventurer
I'll check the connections but they are always tight/the first thing I check. Never been loose when I checked them. Below is a picture of the Genesis setup. Based off the below picture, any thought on where I should look for ground issue?



131-JKDBK2A-17S.jpg

Genesis website
 

JDaPP

Adventurer
Jeep was parked all day except to back out of garage and the pull it back in. Been about 6 hours (will pull numbers again in morning:
Starting battery:12.56
Aux: 12.7
 

luthj

Engineer In Residence
Okay, so your starter battery is a bit worn down. But not crazy low. Check all the cables, nuts, etc for tightness. Take care not to short circuit anything! This means all the ground straps as well as the ACR and battery terminals.

If nothing is obviously wrong, Have someone crank the engine with your volt meter on the battery terminals. Watch what the lowest value is. It will probably be around 11V. You may need to crank it a few times to get a good reading depending on how fast your meter is. If your meter has a min/max recording function you can use that.
 

NatersXJ6

Explorer
I’ve had similar no-starts on my 2014 and found a barely perceptible movement in the negative cable clamp. It sounds to me like you are restoring a bad connection when you move batteries. When you say the terminals are tight, have you also checked the “other end” of the negative battery cable? It might be loose or corroded.
 
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