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.