I'm passing on the credit/blame to @Papa Lazarou. We went camping with him once and he had a battery pack with a fold-out solar panel, and I had battery pack envy.
Just some maths for you @Herr Tubthumper...
iPhone 15 / 15 Pro c3,300mAh
iPhone 15 Pro Max c4,400mAh
Typically, you get about 2/3 of the stated capacity of a battery pack due to power inefficiency, so a 10,000mAh battery pack will charge an iPhone 15 or 15 Pro twice, give or take, and a 15 Pro...