The Pop has an 18,000mAh battery compared to the iPhone X's 2,716mAh battery. That means the Pop's battery is more than six times larger than the iPhone X's. With that in mind, the Pop is actually quite slim — it's surely thinner than six iPhone X phones stacked together.
Energizer says the Pop can hold a 90-hour phone call on a single charge, whereas Apple touts a measly 21 hours for the iPhone X.
The Pop is also good for 100 hours of music playback (the iPhone X gets 60 hours), as well as two days of video playback (iPhone X gets 13 hours). It's not clear if Energizer's claim is based on video stored on the Pop itself, or whether it's streaming video — from the looks of it, it's probably referring to locally stored video.
On standby mode, Energizer says the Pop can last up to 50 days, or about a month and a half. The company doesn't mention what kind of battery life to expect on normal daily usage, but I'd estimate about a week.