Just spoke with the Chevrolet dealer and they have three listings for my 03Z. 630, 650 and 700 CCA. The service manual shows 500 with a note to set a parameter to 600. Which is the correct battery?

 

I believe that 600 CCA is correct. BUT, more important is the reserve capacity, believe it should be 120. These cars use batteries while sitting, consider a battery maintainer if your's often sits for more than 3days.

Also consider a AGM battery that won't leak acid, your computer is under the battery and the wiring harness can be ruined if the battery leaks.

People can correct me if my numbers are wrong.

 

With a 500 as a bare minimum, a good rule of thumb is: buy the highest CCA rated battery you can afford and the RC will take care of itself. RC always goes up right along with CCA numbers.

A higher CCA translates to much longer battery life since it has extra reserve power if needed. That's why you typically see the 6 or 7 year warranties on the higher CCA units. I would recommend 700 at least.

Me, I prefer 800 CCA and 135 RC minutes.

 

Thanks for the replies. Went with the 650 as the 700 was on back order. The optima which the PO had put in wouldn't start the car if it was sitting for more then a few days. Drove it last Thursday and this Tuesday I had to charge it for 20 minutes to get the car to start. Put the charge on last night with the battery disconnected and then did some dark current load testing. I was only reading microamps after a few minutes. You could see the PCM or something must have been loading software and causing the current to jump around a bit. Once that was over it flattened out. Certainly not enough to drain the battery. I checked the Optima's voltage after the testing and it was down to 11.4, not good. Hopefully this is the end of my troubles.

 

If you plan on keeping the car, check out the Sears Platinum Diehard.
Around $200 but 4 year replacement warranty and I believe 800 CCAs.

 

For a 1997 to 2000 it takes a 78 series battery. But you can use a a 75 series battery. For 2001 to 2004 it takes a 75 series. In my 1998 I went with a 78 series because it had 120 reserve minutes, more than the alternate 75 series battery. I got an Energizer at Sams Club for 84.00. 96 month warrenty.

 

I just installed an AC Delco group 78 7YR battery; RC 110, CCA 800 in my '02 Coupe. Fits fine, the RC is pretty close to the recommended 120, the CCA is great, and it's hard to beat the warranty.

 

My 2004 takes a 86 series top mount only battery. I beleive this is the only year that uses the type 86.

 

Your car did in fact come with a top post battery, however the 86 (top post) and 75 series (side post) share the same physical sizes and there are 75/86 series dual-terminal batteries available. The 75 and 86 are the baby-brothers (physically smaller) of the 78 and 34 series.

A group size 78/34 will also "fit" (physically) nicely and being a dual-terminal design, you can use the top posts instead of the side posts on the battery. The 78 (side post) or just a 34 (top post) being slightly larger physically, typically has more CCAs overall. A Sears Platinum Die-Hard P-1 series 34 (big brother to the 86) has 850 CCAs and 135 mins of RC for example and will drop right into a 2004 Vette.

When it come to batteries, a car does not know what size/type/brand of battery it has installed in it, nor does it really matter as long as it provides a) compatible terminal configuration, b) compatible physical size (i.e. physically fits the battery tray) and c) at least a certain minimum "capacity", measured in "CCAs" and/or "RCs".

Also, the thing I like about dual-terminal batteries is if I'm using the side terminals, it give me top terminals to use for charging/jump starting/hooking up aftermarket accessories, etc if I desire.

HTH