I installed a new DieHard Platinum (from Sears) on 8/25/12 (see image below). This has been the best battery I have had in the C5 the past 16 years. Even though it was re-branded as "DieHard" by Sears, it is actually an Odyssey Extreme 34/78-PC1500DT.

I was planning on replacing it after about 4 years to be on the safe side as I drive my C5 every day (and 4 years was up a few months ago). After two AC Delco's and two optima Red Tops, this was the best and highest rated by far in terms of CCA and RC. It also is physically a larger battery than what was recommended for the C5 both by Sears and Odyssey. It is a tight fit, but it worked fine without alteration (for me as well as several C5 owners I see here on the Forum).

The past few weeks, I noticed that it felt like my battery was slightly struggling to start the car. It never really hesitated to start, but when you drive something every day you are sensitive to slight variances. I finally put it on the CTEK overnight to give it a full charge and drug out my trusty "Solar BA7" to test it today. Sure enough it showed 12.69V, then it ran the CCA test - 330 (Red Light Failure - Replace Battery). Load Test at the Parts Store said "Battery Good". Once again this Solar unit diagnosed a problem nothing else seems to catch!

So, here was a case where the battery showed good voltage, but not much throughput left in it.

This is also a great video I found that demonstrates what I was experiencing...


Here is what my 4+ Year Old Diehard tested a couple days ago just before I removed it:

 

This is the new replacement Odyssey I received a couple days ago, and right out of the box it tested 354 CCA ABOVE the 850 rating before I even put it on my CTEK charger and installed it in the car!:










I got even better test results after giving it a full charge on the CTEK overnight. Car feels like it starts now before I even turn the key!

 

I too have a Sears DieHard Platinum in my car - been in there since October 2010. I keep mine on a Battery Tender Plus since I do not daily drive the car and so far, knock on wood, it has not shown any problems.

Good that you were aware of even a slight issue with starting the car. Where did you get the Odyssey battery at? I've been very pleased with the DieHard and since Sears does not carry the Platinum series any more, I'd like to know just in case I need one anytime soon.

 

The lowest price I found was at APEX Battery, but they were back-ordered for several weeks, so I cancelled that order and placed another order with 4WheelParts.com. I have ordered other hard to find parts from them I the past (like my 135/90 watt H4 headlight bulbs for my Euro-Headlamps). Their price was only a few dollars higher than Apex and I ordered it Monday afternoon and it arrived before noon on Wednesday for $16! Battery weighed 49-lbs.

Who knows, the 4 year old battery may have still started the car for months or years longer, but my experience with my previous batteries in my C5 is that after a few years other unexplainable nuisance issues start popping up that installing a new battery always seemed to fix for me (like mirror memory settings not holding and the like). My two previous red-tops never failed to "start" my car, but I did experience other unexplained electrical issues after a few years.

 

It's always been Amps !!!!

 

After all, you can't eat it, smell it or have sex with it.

 

There was another post about this same battery just the other day. I too had one and it want to shlt in less than 2 years. I am DONE with Sears for anything other than Craftsman.

 

you can have volts but no current

 

I also replaced with a 34/78 battery. It's from Batteries Plus. 850 CCA. Like you said bit of a tight fit but sits solidly in the tray. Cable connections were a small challenge since 2004 uses top mount cables. Posts on 34/78 are center line, original posts are along one side.

 

Interesting....Looks like I got to get me a Solar BA7 tester.

 

Is the Odyssey an AGM battery? I keep reading that it is better to have since the can't leak.

 

Yes, it is. They are the company that was manufacturing the PLATINUM series Die-Hard batteries for Sears for several years.

I've had the same Die-Hard Platinum battery for several years that Choreo and Vetteman Jack both have.
Come time for replacement, I'm going with the Odyssey. It is a premium quality battery made in Missouri by Enersys Co.

HTH

 

My Platinum has been in there since 2008. No signs of any problems yet - that statement has probably just put a spell on it! I will most like go Odyssey as a replacement.

I did read on a boating/sailing forum that the reason Sears dropped the Platinum was their generous warranty (free replacement for 4 years, or so), and the boating fraternity were treating them as deep cycle batteries and they were failing (and being replaced) within warranty.

Whether that's the real story who knows, but a number of people quoted Sears parts counter staff as saying they were dropped because of warranty costs.

BTW, the "big" 78 battery was the OEM size for early C5's, they got a size smaller in later cars.