I needed a "battery case" for my iPhone 8 very shortly after I got it and so did my wife.

She just upgraded to an iPhone 12 so we'll see how much time goes by before she needs one again too. Luckily Apple is making one now, so hopefully it will work better than the third party ones with respect to using the lightning port pass-through, which sometimes fails.

If needing more battery time were the only thing stopping me, I'd be on a PinePhone today.