The One Item You Should Buy at Costco Instead of Walmart, Experts Warn

You should always buy batteries in bulk.

Researchers for MagnifyMoney, a personal finance service from LendingTree, released a report on Sept. 13, comparing the bulk prices for several items at Costco to regular sizes of these items at Walmart. According to their findings, batteries had the largest difference in savings for bulk and non-bulk shoppers. At Walmart, an eight-count pack of Duracell AA batteries typically costs $7.47, while a 40-count from Costco is $17.99. So at Walmart, a pack averages out to around 93 cents a battery, while the 40-count pack from Costco is only about 45 cents a battery.

The researchers say buying batteries in bulk would equate to a substantial savings of 52 percent. "Shoppers who go with the smaller size may find themselves returning to the store sooner than they’d like and—in turn—paying more for batteries," the report states.

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There are other items you could save money on by buying in bulk.

Batteries may give you the most in savings when it comes to buying at Costco instead of Walmart, but there are other items you may want to buy in bulk, too. According to the report, consumers can also save 50 percent when purchasing a 24-pack of bottled water at Costco compared to just a single bottle at Walmart.

But overall, the researchers say that Ziploc freezer bags might be the "best bulk deal for the money and versatility." According to their findings, you can get a savings of 45 percent by buying these bags in bulk rather than in a standard box.

"Since the bags won’t go bad, a 152-count box may be worth the upfront investment of $17.49, compared to paying $4.32 for a box of 20 bags," the researchers said. "Use the bags to store food, household items, toys, or other small goods to get the most out of a bulk pack."

Toilet paper is the only product that had no real difference in price.

You probably don't need to try comparing prices and quantities when it comes to toilet paper, however. According to the report, this is "the only product that offered no difference for bulk and non-bulk shoppers." The researchers looked at 12 and 24-count rolls of Seventh Generation toilet paper and found that customers were paying the same price overall either way. The toilet paper came out to be about $3.28 per 100 square feet, even after the MagnifyMoney researchers looked at prices from different retailers.

But they say there may still be benefits from buying more toilet paper at once. "While shoppers might not save on the bulk purchase, fewer trips to the store to buy toilet paper could equate to savings on gas or the impulse purchases some shoppers make when they visit a store to purchase a single item," the researchers said.

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But you shouldn't buy everything in bulk quantities.

The researchers say shoppers should still consider the practically of buying in bulk, despite the potential savings they could get in cost. According to their report, shoppers can save 40 percent on mayonnaise by buying it in bulk at 64 ounces, but that might be a lot of mayo to use before its expiration date, even for a family.

"What’s the point of buying in bulk—and ostensibly spending more money—when you don’t get around to using or finishing the items you buy?” Ismat Mangla, MagnifyMoney's senior content director, said in a statement. "Then you are simply spending more and wasting that money."

You should also consider the cost of an annual membership to Costco, which starts at $60 a year. "If you’re spending $60 a year on a savings club membership, will you spend and use enough to offset that $60? You really just have to think about your personal spending, do the math, and figure out if it’s worth it," Mangla said.

RELATED: If You Bought This at Costco, Stop Using It Immediately, Authorities Say.