Our 2004 only has 27000 miles but was thinking of replacing the battery since it is at least 6 years old.Do you really need to use the more expensive battery that goes under the back seat,I wish they hadn't done that,its nearly twice what the under hood battery would be.

Yes, and it needs to be the vented one. OR you will be breathing the charging fumes. No way around using the one listed.

Check around there are numerous normal priced batteries that are set up with the vents in the top of the battery. I know I have seen them at Oreilly, Sams Club and Walmart. You can even buy the more wider more cranking amp batteries with vent holes and get them to fit under the seat. I did that. The only thing that I had to modify was the rubber strap between the rubber hoses. I cut it in half so that it would make attaching the hoses to the vents easier. Then I used duct tape to make sure they stayed attached. Not worried about the tape ever coming loose because there is no moisture, dirt or oil that ever gets under the seat. My original battery lasted 9 years. I would attribute that to the battery never being exposed to any harsh elements.

Autozone has the replacement as well (Duralast), and we have had several members buy and recommend it. Probably what I will go with. Mine is showing it'* age at 5 years. I am prone to leaving my GXP under a cover for a week or two at a time. And find the battery dead. If I drive it frequently, it'* OK.

AC Delco Batterys are not of the rigid quality of years past. The Division was sold to Johnson Controls several years back by Delphi. They make average quality batterys and also make the Duralast.

In fact, they have pretty much stapled together the largest battery production Company ever. All these batterys are now the same as far as manufacturer and design, regardless of what color and label you may think better :

OEM GM, DaimlerChrysler, Ford, Honda, Nissan, and Toyota

These Stores:
AutoZone, Interstate Battery, Sears, Wal-Mart, and Costco

Carrying these Brands:
DieHard, Duralast, Interstate, ProStart, and Everstart

They also just captured the OEM Europe Market buying up HOPPECKE Automotive GmbH & Co.

They also manufacture the Optima Line of spiral wound/glassmat batterys.

Battery life and quality can be misleading because of the manufacturing process, time left in storage, and shipping and handling before it gets installed in your car. But most are same/same these days as shown above.

Have the battery tested. I bet you do not need one yet.

Thanks for the input I went for a group 97 about 2" wider with more cranking amps and reserve,and cut the vent strap as mentioned in an earlier post,and duct taped the vents on the battery.This battery was $96.00 at Sam'* club instead of 135.00 other places for the original 100 battery.The car sits quite a bit and when I did drive it the volt meter showed about 16 volt charge so I think the alternator was being worked a little hard,thought I would just replace it after 6 years could leave you anytime.