I always own at least one that can give a full charge to my phone and also be small/light enough to throw in a purse, and then I own a couple high output/larger/heavy banks to be used for emergency power in the event of, like, a couple days worth of electricity being out
@ThunderChicken A lengthy power outage would be the only possible scenario where I could see that I might have a use for a power bank. I have been without power for a couple of days at a time, but merely charging my phone occasionally in the car was enough to keep it near 100% for the duration of the outage.
wearable? Multipurpose? My main problem with power banks is that they are inconvenient which is a shame for a technology intended to be convenient. I have to remember to charge them and then I have to remember to carry them around with me on the extremely rare occasion that I actually need it. If someone added power bank functionality on something I otherwise actually have a reason to carry around with me, then maybe I would actually use it.
My phone has a 5000 mAh battery. I am a minimal user of my cell phone, so a full charge often lasts almost a week. These days I am not often away from home and I can charge my phone in my car when away if needed. Why do I need a power bank?
Living out in the country, we have at least one 12+ hour outage per year. So we have a couple of power banks I made from old car batteries on float chargers out in the garage (deep-cycle would obviously be better, but these were basically free). Plus every vehicle on the property has USB powerpoints (even the lawnmower and the tractor), so we can tap off of them with minimal fuss. Output over convenience any day.
(And if it’s really bad, any of the vehicles can be used with a power inverter as a makeshift-but-inefficient generator. Also handy when I want to use power tools on the far end of the property.)