Heavy iPhone users can finally breathe a sigh of relief.

Apple has just unleashed a new Smart Battery case for the iPhone 6 and 6s that nearly doubles the device’s battery life.

Available for $99 in either white or black, the new silicone case features an integrated battery in a bump out on the back that Apple said provides the phone with enough extra juice for up to 18 hours of LTE internet use, 20 hours of video playback or about 25 hours of talk time.

According to specs for the iPhone 6s, the device’s standard battery offers up to 10 hours of LTE internet use, 11 hours of HD video playback and 14 hours of talk time without extra support from the new case.

The case is Lightning accessory compatible, and can be charged simultaneously with the iPhone itself. When the case is attached to the phone, the case’s battery status is displayed on the lock screen and in the notification center.

But there are a few small catches. First, those who enjoy the iPhone 6’s super slim design may be put off by the case’s battery bump, which nearly doubles the phone’s thickness.

Second, and probably most important, Apple has included the disclaimer that its extended battery claims “depend on network configuration and many other factors” and said actual customer results may vary.

Apple said it conducted its tests with auto-brightness disabled and almost all other settings on default. The video test included looped playback of nearly two-and-a-half-hour movie purchased on iTunes, and internet tests used 3G, LTE and Wi-Fi networks to browse “snapshot versions of 20 popular web pages” and check email once every hour. Talk tests consisted of placing cellular phone calls, so the impact of using Wi-Fi calling is unclear.

Apple’s new case joins a number of other – cheaper – iPhone battery cases on the market, including those offered by Tylt, Anker and ZeroLemon.

The Smart Battery case is currently available in select Apple retail locations and in the Apple store online.