By Mitch Lipka, dealnews Contributor Evan Krell via FlickrWhen it comes to batteries, how can you tell a deal from a dud? When is it worth spending money on a premium brand? We brought a collection of different AA batteries to the Worcester Polytechnic Institute and asked if they could test to find out whether there's any real difference between brand-name and generic batteries. The answer is that you're better off buying less expensive batteries, such as Rayovac or generics, or getting regular Energizer or Duracells on sale, because our exclusive tests show there is no measurable difference in quality among these batteries. That's right, none. So just buy whatever is on sale, take steps to make them last longer and never fret again about what type of battery to buy. At least that goes for regular batteries. The very notable exception: The Energizer Advanced Lithium battery separated from the pack like the bunny that promotes the brand. Not only did that particular battery push out far more initial voltage than the others — when it finally corrected down to the expected 1.5 volts, it kept going and going and going. Here's how our test worked: A team of graduate and undergraduate students supervised by Prof. Glenn R. Gaudette at the renowned eponymous institute in Massachusetts put several sets of batteries through the paces over several months. All the batteries were purchased off the shelf at retail. Among the batteries tested were Duracell Ultra Advanced, Duracell Coppertop, a generic battery, Energizer Advanced Lithium, Energizer Max and Rayovac. All were measured for their initial voltage and how much energy they lost over 19 hours of constant use. After 19 hours, the Energizer Advanced Lithium battery was still running at 1.5 volts — far higher than any of the other batteries. The WPI team said that it showed "remarkable stability" compared with the rest. The testers said there was no statistically significant difference between the other batteries. (See charts below.) So, why not just buy the Energizer Advanced if it did so much better in the tests? Price. You get more; you pay more. But do you get four times more? Our latest price-check shows that Rayovac AA batteries were selling for a quarter of the price of the top-performing Energizers — 42 cents each vs. $1.42 each. The testing team also expressed some concern that some very sensitive devices could be negatively affected by the higher-than-expected initial voltage. The WPI folks caution that the testing included only the pressure of constant demand — not the on and off usage that can be seen in real life. Here is a survey of average battery prices, per battery, for the various brands tested: Duracell Ultra Advanced: 91 cents Duracell Coppertop: 59 cents Generic: 53 cents* Energizer Advanced Lithium: $1.75 Energizer Max: 68 cents Rayovac: 42 cents *Price at local store. Check out our current best deals on batteries: Energizer e2 AA Lithium Battery 8-Pack for $10 with free shipping Sony Rechargeable 2000mAh AA Battery 4-Pack for $7 + free shipping 24 Rayovac NiMH AA Rechargeable Batteries for $40 + free shipping Deals change often, so be sure to check prices before you buy. If you want to find out about the latest battery deals, download the new dealnews iPhone/iPod app and get alerts sent to your mobile phone with the latest pricing information. Or, check out all of our Battery deals for more powerful sales. Figure 1. Initial voltage in AA batteries. All batteries had a similar starting voltage with the exception of the Energizer Advanced Lithium, which had a significantly higher initial voltage. Credit: WPI. Figure 2. Changes in voltage over time. Energizer Advanced Lithium started at a higher voltage, had the largest initial drop in voltage but ended with a higher voltage compared with the other batteries tested. Credit: WPI. Mitch Lipka is an investigative journalist for consumer issues who formerly wrote for WalletPop.com, Consumer Reports, The Philadelphia Inquirer, and the Fort Lauderdale Sun-Sentinel, among other places. Follow him on Twitter at @mitchlipka or on Facebook. Follow @dealnews for the latest roundups, price trend info, and stories. You can also sign up for an email alert for all dealnews features.