Posting this hoping to get some feed back since I'm now arguing with sears and posted on THENEWX. Let me know what you guys think. Normally I wouldn't give a crap but the battery was like $250 and still under warranty for a year.

Purchased a diehard platinum agm about 3 years ago,never had a problem until this year. First real cold day, single digits,truck would crank but not start, jumped it ,started right up, that was 3 weeks ago. Figured it was a fluke, since then my terminals were a little dirty so replaced both with brass, like many have here. Charged battery, everything was good, had a cold morning again, wouldn't start, jumped it, ran fine. I pulled the battery ,brought it to sears, they test it,says good. OK..wtf...I deal with it,charge it again,seems fine.. Yesterday, 12* out, tried to start it, cranked real slow then finally started.. I pulled the battery, I showed 12.48 volts, I let it sit overnight out of the truck, tested this morning, 12.32 volts. I brought it to advance auto ,they tested it, 12.32 volts, 607 CCA down from 740 and showed good but needed a charge. I brought it directly to sears, they tested it showed good but needed a charge, their tester doesn't give data,only shows good ...
So, proceeded to discuss with manager, I showed him the data from advance, he agreed, ratings are low for the battery but his tests show good,so pound sand basically..
He insists there is something wrong with my truck and said I should replace the starter, yeah right... From research, this agm battery should rest at around 12.8 volts and not really loose a charge, no clue why CCA is down to 607 from 740,sears didn't know why either. And why it dropped from 12.48 to 12.32 overnight, I think the battery is failing. Any thoughts?
Oh, has a 4 year full replacement warranty and I'm year 3 also..also, I have a bulldog and my voltage when driving is 13.8- 14.2, so alternator seems fine.

First thing I would do is to check for any parasitic drains, such as lights, radar detector, CB, etc. that could be drawing down the battery. Check to see if there is any current flowing out of the battery when your truck is shut off.

k_enn

Good point Kenn
also..

The battery may have a cell going bad where it only shows on extreme conditions.
and under load. Then when it sits or warms up the condition is masked.

Try another battery / spare in the X under the same conditions and see if it is the same.

The other thing to do is just wipe it out.. pull your self down the block with the winch and lights on engine off and see if it wipes out completely . problem is solved it won't take a charge then.
todays testers are setup to test other batteries and their own
with different spceks for both. It happens a lot at work.. you want to swap out the battery and it tells you to charge and retest,

Good Luck Tony

If it has a 4-year warranty, and you're only 3 years in, then why are they even giving you crap about it? Just have them replace it under warranty.

IIRC, the warranty is pro rated. The longer you are into the warranty period, the less you. I would suspect being 3 years into a 4 year warranty on the battery, you would not get much.

k_enn

k_enn, Tony may be wrong, but he posted "has a 4 year full replacement warranty and I'm year 3" Full replacement not pro rated.

Scott

The problem with sears swapping the battery is their tester is showing the battery as good. I agree with Ernie, put a large load on that "good" battery and kill it. Discharge and recharge it a couple times and hopefully the battery won't be able to put out enough amps for their testers to pass it.

Correct full 4 year replacement and sears won't replace if their tester shows good. My winch isn't hooked yet, I'll figure out some way to drain it and see what happens.. Slow start this morning and 0* this weekend so well see.

Quick update, sears agreed to replace it but they don't make them anymore. Went with their gold series agm in a 34r

Nice! Good to hear, Tony.

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Awesome