If the first rule of Pokémon Go is "Gotta catch ‘em all," the second rule is you are going to need to bring an extra battery to do so.
Therefore, it’s no surprise that the success of the power-draining app has led to a surge in sales of external battery packs. In fact, sales over the last two weeks are double those of a year ago, with 1.2 million portable battery packs sold, according to NPD.
As for why the app is such a big battery hog, it relies on constant use of GPS and motion sensors, which are themselves power drains. Throw in real-time gaming and some augmented reality and it’s easy to see how things quickly get into the red.
"As a way to compensate for the extra battery usage, consumers are buying portable power packs so they can continue to play, uninterrupted," NPD’s Ben Arnold said in a statement.
Mobile phone carriers and retailers have been looking to cash in on the trend, offering discounts on the accessories as a way to lure players into their stores. They’ve also been using actual lures.
Meanwhile, Pokémon Go does have a battery saver mode that dims the screen and makes other changes to preserve juice, but it temporarily pulled the feature from the iPhone version of the app due to bugs.
This article originally appeared on Recode.net.