Apple's new iPhone case will give you about an extra day of battery life, but it's quite bulky
https://www.cnbc.com/2019/01/20/iphone-smart-battery-case-review.html
Apple on Friday began selling its new smart battery case for the iPhone. I've had one for a couple of days and have been testing it with my iPhone XS Max.
The accessory, which costs $129, is also available for the smaller iPhone XS and the more affordable iPhone XR.