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Discussion Starter · #1 ·
Hi I'm new to the forum and new to diesel trucks so I would appreciate some help. I have a 95 with 170xxx on it. It has a new glow plug relay and alternator. I had some shifting issues recently and replaced the neutral safety switch... all problems resolved. However it just started draining my battery (it only has one right now, the other tested bad). I can start the truck and pull the battery and it runs under it's own power. With a multimeter (grounded to the negitive battery post without a battery) it has 14 volts coming off the back of the alternator, at the starter relay and at the positive battery post. I heard there was a under hood fuse #6 that could cause a problem, It checked out. I'm at a loss and very confused. If anyone has any ideas. Please suggest them
 

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Is the new GPR factory or aftermarket? With the key OFF, there should be voltage at only one of the large terminals. With key OFF, what is the amperage draw on the battery (put multimeter in line with disconnected battery cable and the disconnected post)? If there is a draw, disconnect wiring from the alternator and see if it goes away or drops significantly. After that, its a process of removing fuses to see which circuit is causing the problem. I would also have the remaining battery retested as using only one battery is going to put a lot of stress on it (really should get 2 new ones). Cheers!
 

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I can start the truck and pull the battery...
That's VERY bad for the alternator & everything electronic on the truck. Don't do it any more.

Since you already seem to have the battery out, LEAVE it out (engine OFF), charge it <5A for a day or so, measure & record its voltage, again after it sits for ~10-60min, and once more after a day. Do not beat, drop, or vibrate the battery any more than is absolutely necessary. Post your results. A quicker way to test it is (after charging) at any dealership with a MidTronics high-frequency tester, similar to this one:

 

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I'd be willing to bet that if one battery went bad, the other is failing now too, esp. if it's been tasked to start the engine solo. HF (^^^^^) or load test would be telling, but since you need one battery anyway, it'd be prudent just to install two new matched batteries.

If you suspect the battery/batteries being drained while the engine is OFF, that's a whole different challenge with different tests. You need to test for current draw, and start pulling fuses until the draw goes away.
 

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Discussion Starter · #5 ·
I am going to try to load test the battery with it out of the truck this week. However I grew up on carbureted motor so forgive me electronics is not my strong suit. My glow plug relay is after market the truck was stock with a two post and wiring harness until last year when I replaced it. But it is working (only power to both posts for thirty seconds or so when I first turn on the ignition). The thing I can't wrap my head around is if the truck can run on its own (without battery) how can anot her fused component be drawing enough power to not at least give the battery a charger to keep it somewhat full? Because if I let the truck run for an hour the battery is barely strong enough to keep my can lights on after I turn it OFF. where is all the energy going?
 

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Because if I let the truck run for an hour the battery is barely strong enough to keep my can lights on after I turn it OFF. where is all the energy going?
The battery could be toast.
As was mentioned above--buy two new identical batteries.
 

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Discussion Starter · #8 ·
Okay everyone says bays battery so that's where I'm starting. It's still under warranty so I'll replace it and get another matching one. I'll post an update this weekend. Thanks everyone
 

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Okay everyone says bays battery so that's where I'm starting. It's still under warranty so I'll replace it and get another matching one. I'll post an update this weekend. Thanks everyone
Wait :winking:

We are saying batteries.

A matching pair of two new batteries.

You said your one battery tested bad. One bad battery can often fry the other good battery. Now if you only replace the first battery then it will get overworked because the second battery is now toast.

Then the assumption is made that the issue must not be the batteries because they have each been replaced recently...but if they are not replaced at the same time then they can still be the issue.

Clear as mud :winking:

Cheers
 

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Buying 2 batteries on the same day is no guarantee that you're buying batteries that were MADE the same day, or that they have the same voltage, or the same CCA/CA, or the same Ah/RM, or the same anything. And every vehicle & battery manufacturer whose battery testing & warranty procedures I've read specifically DISCOURAGES load-testing them for any reason. They all require a MidTronics high-frequency tester's warranty code.
 

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Buying 2 batteries on the same day is no guarantee that you're buying batteries that were MADE the same day, or that they have the same voltage, or the same CCA/CA, or the same Ah/RM, or the same anything. And every vehicle & battery manufacturer whose battery testing & warranty procedures I've read specifically DISCOURAGES load-testing them for any reason. They all require a MidTronics high-frequency tester's warranty code.
Steve,

Yer killin' me :winking:

It is reasonable to say that buying two new "identical" batteries is a pretty safe bet.

I don't think it is necessary for batteries to have been manufactured on the same day. Nor is it important that they have the same voltage because the first thing to do when you buy a new battery is to charge it with a 120v battery charger when you get home.

I am just trying to let the OP know why the common practice on a dual battery system like ours is to replace in pairs.

Steve, your battery tester is a really cool tool and I wish I could afford one, but batteries can still be perfectly good without one. My batteries are happy as clams.

Every month I charge them with a 120V charger. Every few months I clean my batteries with a baking soda solution and I remove oxidation at the posts and just like plants, it really helps if you talk to them.

(Note: batteries often have a little round circle with a month/year. I used to think this was a manufacture date but it is not. It simply reflects the last time the batteries were charged. A shop that sells batteries typically has a large inventory and every couple of months, the batteries with the oldest little round circle will be serviced. This might include checking electrolyte level and a visual inspection as well as topping off the charge. When that is done then a new little round sticker replaces the old one. Now the big sticker on the top with the holes that can be punched out? Those are removed at the time of sale for an easy reference for warranty purposes. Many times the salesman does not bother to remove the little date holes because they insist you bring in your paperwork for warranty anyway. As we all know, the warranty is non-transferable, it is only valid for the name on the sales receipt.)
 

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If "new identical" is enough, then why isn't "new" enough? What would be wrong with a new MotorCraft Gr.65 850CCA and a new DuraCrap Gr.78 650CCA? They're both 12V batteries, right? They'll both hold a 12V charge & put out some amps, right?

My point is: if you think "matched" batteries are somehow better, then you have to get MATCHED batteries. And that means testing them with a reliable tester before buying them. The only type of tester recognized universally by battery & vehicle mfrs. is the kind I linked.




Personally I don't think it's important to match batteries. I mix ages, brands, & sizes, but my Bronco isolates them when I turn the key off, so it's not comparable to your diesels. (I sold the 6.5L in my avatar.)

When I want them in permanent parallel, I make sure they HOLD the same voltage (within a narrow margin). Charging is irrelevant - it's what the batteries do when they're NOT being charged that matters to how they interact with each other. Age, brand, CCA, CA, RM are all irrelevant. Only resting voltage (AFTER they're fully charged) matters.
 

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If "new identical" is enough, then why isn't "new" enough? What would be wrong with a new MotorCraft Gr.65 850CCA and a new DuraCrap Gr.78 650CCA? They're both 12V batteries, right?

Personally I don't think it's important to match batteries. I mix ages, brands, & sizes, but my Bronco isolates them when I turn the key off, so it's not comparable to your diesels. (I sold the 6.5L in my avatar.)

Age, brand, CCA, CA, RM are all irrelevant.
Steve,

I would be glad to carry this debate on in message format.

The OP is new to the dual battery Diesel system and that is what he owns so a discussion about your own system with the "isolation" feature seems to confuse the topic.

Hopefully the OP understands the importance of buying a pair of batteries that are equally matched in atleast CCA and CA and hopefully specific brand and model as well.

Good luck to the OP in whatever he decides. :thumbsup:
 
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