One minute, your iPhone 7 says it has a 50-percent battery charge; a minute later, your iPhone is as dead as a doornail. Sound familiar?

A portable USB battery pack makes for a handy way to charge your iPhone on the go, but then you’ve got to remember to keep the charger on you. An easier way to keep your iPhone happy, healthy and charged is to go for a case with a built-in battery—nice, but at up to $100 each, they can be pricey.

Luckily, Trianium’s charging case for iPhone 7 is on sale for $40, or half off its usual $80 list price. The slim but durable Atomic Pro case can double your iPhone 7’s battery life, according to Trianium, meaning you can chat or crank tunes on your AirPods or Bluetooth headset all day without worrying about your iPhone’s battery conking out. (Still using a wired headset? I’ll keep an eye out for an iPhone 7 charging case that’s compatible.)

This $40 case is specifically designed for the iPhone 7, but Trianium also offers an iPhone 7 Plus version for $50.

Check out the Trianium Atomic Pro iPhone 7 Portable Charging Case on Amazon!

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