Our latest tests show that shopping for a car battery by brand name alone can be a big mistake, both in terms of performance and in cost. But our latest Ratings make it easy to find the best one for your needs and budget, no matter what you drive.
Big-name battery brands DieHard (Sears and Kmart), EverStart (Walmart), and Interstate all top our Ratings in some group sizes, but they are at or near the bottom in others. The greatest inconsistency comes from DieHard, which makes both the best and worst performers in two of six common sizes. Based on our findings, it is best to cast aside brand loyalty, and instead focus on CR's test results. (See which car batteries we recommend.)
For instance, a DieHard Advanced Gold battery now tops the top-terminal Group 65 category used in many large vehicles, with no evidence of the small case cracks seen in our last test. (The cracks observed in our previous test caused no loss in performance, but previously resulted in a lower score.)
One of our evaluations, called a "life test," involves repeatedly draining and recharging batteries while they are immersed in 167-degree water—a protocol based on an industry test. This simulates the taxing cycles batteries go through while subjected to high underhood temperatures. We extended the test from 10 to 15 weeks last year, to more accurately reflect battery life over a longer period.
Two samples of the DieHard Advanced Gold 50748 in Group 48 failed this test after just six and seven weeks—not even halfway through our stringent test regimen. Two more examples purchased for retesting also failed.
The failures are especially noteworthy because the DieHard Advanced Gold is an AGM (absorbed glass mat) design, which typically makes for a more rugged and longer-lasting battery than a conventional battery. Our test samples of the DieHard Advanced Gold 50748 were the only AGM batteries that did not to survive on average 13 weeks or more of the life test, and they would not have lasted even through the old 10-week test. All other AGM batteries in this test scored much better in the life test.
AGM batteries also typically cost more than conventional designs, and only one other battery in our Ratings carries a higher price than the $180 we paid for the DieHard Advanced Gold 50748.
If you're shopping for a battery, the best bet is to check your owner's manual for the size you need, and refer to our ratings for one that suits your needs and budget—regardless of brand.
We do see significant variation in how models perform year to year, reflecting production changes. So, it is crucial to check the Ratings right before you buy, rather than count on data from a year or two ago. A quick check of the car battery Ratings can ensure you get more performance for your money.