My OEM battery started showing signs of age last winter; with winter approaching, I'm thinking it's time to replace a more-than-four-year-old original battery.

I autocross in stock class, so I need a battery similar in size and weight to the OEM one. Should I just buy one at Costco, or is there some reason to pay Sears a lot more to do the testing/installation?

 

Do some searching and you'll find that automotive batteries are made by three companies period (Delphi, Exide, and Johnson Controls Industries) with two being predominate. So it matters little whose name is on the battery. More important are warranties, replacement access when out of town, etc. With all that said, I just replaced my OEM one with an Everstart 51-4/435CCA battery from WallyWorld. It meets your track criteria as both it and the original Panasonic are both Group Size 51R.

--Bob