Is Costco's Interstate battery better than AutoZone's Duralast?

This specific test did not physically bench-test Costco's Interstate battery, so there is no direct measured comparison to Duralast to report. What the test does show is that Duralast, despite costing 40 dollars more, is made by the same manufacturer (Johnson Controls) as the budget EverStart and performed slightly worse at room temperature. The tester's own recommendation leans toward whichever option, Costco's or Walmart's, is priced lowest.

Is AutoZone's Duralast battery worth the extra price over EverStart?

Based on this test, no. The two batteries are made by the same manufacturer and look identical apart from the branding stickers, yet Duralast costs about 40 dollars more and performed slightly worse on the room-temperature cranking test. The tester explicitly recommends against paying that premium.

Are AGM batteries worth it over a standard flooded battery?

It depends on your needs. AGM batteries handle vibration and deep discharge better and can show lower internal resistance in the cold, which matters for start-stop systems and heavy electrical loads. But in this test, the two AGM batteries did not beat the budget flooded EverStart on raw cold cranking output, so AGM is not an automatic upgrade for a standard car.

How do I know which battery brand actually made mine?

Check the case for a manufacturing code or ask the retailer, since many store-brand batteries are built by the same handful of manufacturers (Johnson Controls, East Penn, and EnerSys all appear behind different brand names in this test). Knowing the actual manufacturer can reveal when a pricier badge is selling the same hardware as a cheaper one.

What matters most when picking a replacement car battery?

Group size fit comes first, since a battery that does not seat correctly is a non-starter regardless of brand. After that, buy the freshest battery you can find (check the date code) and weigh the warranty length heavily, since a longer free-replacement period is worth real money on a part that eventually fails on everyone.

Did Which Brand Wins run these battery tests?

No. Every measurement in this guide comes from Project Farm's independent hands-on bench test. We index the results, summarize what they mean for a buyer, and link straight to the source so you can watch the full test yourself.

AutoZone vs EverStart: 6 Car Batteries Actually Tested

Every big-box store and auto parts chain wants you to believe their house-brand car battery is the smart buy: Costco pushes Interstate, AutoZone pushes Duralast, Walmart pushes EverStart. The batteries all sit in the same aisle claiming similar cold cranking amps for wildly different prices, and none of the shelf tags tell you which one is actually made better.

So which one holds up when you put it through a real bench test? A hands-on tester bought six popular car batteries, including AutoZone's Duralast and Walmart's EverStart, and ran them through the same freezer torture test. Costco's own Interstate brand was not part of the six batteries physically tested, but the tester's closing recommendation names it directly, and that context matters for anyone comparing warehouse-club batteries to the rest of the field.

Here is the honest breakdown of what was measured and what was not.

What the testing showed

Every figure below comes from Project Farm's independent bench test. You can watch the whole thing on the full car battery head-to-head, which put six batteries through cranking, load, recharge, and freezer testing.

The six batteries were EverStart (Walmart), Optima RedTop (an AGM battery), DieHard Advanced Gold (Sears/EnerSys, AGM), SuperStart Premium (O'Reilly), Duralast Gold (AutoZone), and AutoCraft Silver (Advance Auto Parts). Each went through cranking amps at 75F, a 42 to 44 amp load test for 30 minutes followed by an overnight rest, a one-hour recharge test at 10 amps, and cold cranking amps after 24 hours and then 48 hours in a freezer at 0F and negative 20F.

Budget pick

EverStart

Price shown in test: $119.76

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The cheapest battery beat the AutoZone brand that costs 40 dollars more

EverStart, the least expensive battery in the test at 119 dollars and 76 cents, delivered the strongest cold-weather output of all six. It is made by Johnson Controls, the exact same manufacturer that builds Duralast, the AutoZone house brand priced at 159 dollars and 99 cents. The tester's note on that pairing: everything about the two batteries "looks identical except for the exterior stickers," and Duralast costs 40 dollars more while performing slightly worse on the room-temperature test. The explicit recommendation is to skip the AutoZone premium and buy EverStart if a flooded battery is what your car needs.

Where Costco's Interstate battery fits in

Costco's Interstate battery was not one of the six batteries physically bench-tested in this video. But the tester's closing verdict names it directly as a value option worth considering: "If your vehicle uses a flooded lead-acid battery like the first four batteries we tested, I would continue using a flooded lead-acid battery and would buy either a Costco Interstate battery or the Walmart EverStart if their prices are the least expensive." In other words, the recommendation to consider Costco's battery is based on price and category, not on it appearing in the actual bench data, and that distinction matters if you are choosing based on measured performance specifically.

The AGM batteries did not run away with it either

The two AGM batteries, Optima RedTop (224 dollars and 99 cents, the most expensive of the six) and DieHard Advanced Gold, both carry a real price premium over the flooded batteries. Optima posted the best internal resistance at the coldest test stage, but its raw cold cranking output at 0F still trailed the budget EverStart. DieHard was the fastest charging and best room-temperature performer, but the weakest of all six batteries in both cold cranking amp tests.

How to read this for your own purchase

The test did not crown one single overall winner across every category, and that is the honest takeaway. It landed on recommendations by battery type, and the AutoZone-versus-Costco-versus-Walmart question really comes down to which manufacturer is actually behind the battery you are looking at.

If your car uses a standard flooded lead-acid battery, which most cars do, the tested data says buy on price, not on the store's badge. EverStart matched or beat the pricier Duralast, and both share the same manufacturer. Costco's Interstate battery, while not directly bench-tested here, gets the same price-first endorsement in the closing recommendation.

Before paying an AutoZone premium over a Walmart battery, check who actually manufactures each option. Johnson Controls builds both the EverStart and the Duralast in this lineup, and the cheaper one performed at least as well in the cold.

A few universal rules the numbers back up:

Match the group size to your vehicle first. A battery that does not physically fit is a non-starter no matter how good its brand reputation is.
Buy the freshest battery available. Batteries lose capacity sitting on a shelf, so check the date code before you buy.
Ask who actually manufactures the battery, not just whose name is on the sticker. Several house brands across different retailers come off the same manufacturing line.

Want to compare more of the gear that keeps a car running? Browse the rest of the jump starters and car power tests for chargers, jump starters, and testers put through similar bench work.