About 10-15 years ago the power-bank came on the scene. People were carrying phones and other gadgets around that needed charging and were constantly worried about running out. As a consequence, if you offered them one with your logo, they would carry it around. Marketing objective achieved.
Fast forward to today. The gadgets now have ~3000mAh batteries, and better battery life. But the humble power bank hasn't really kept up. You see, most of them are a single 18650 battery, usually used. Yes, used. This means that some crusty old laptop you had about 10 years ago that was thick enough to have a 6x18650 battery pack was 'recycled'. Someone took it apart, took out those batteries that hardly held a charge, slapped it in some new plastic, and shipped it back.
Let's take a look at one. I attended a conference in early December. The 'swag bag' that we were handed came with the de-rigeur 'power bank' and some sticker thing you put on the back of your phone to make it easier to hold. The power bank claims a (actually believable) 1200mAh capacity. Others are not so held by the truth and use words like '2000mAh', or why not '200 000mAh' 🙂
OK lets think about this. My phone (pixel 2xl) has a 3520mAh battery. This means, in a perfect world, I could get about 1/3 charge from this device. The Pixel 2 XL supports USB-C PD, it can charge 'up to 7 hours of charge with 15min' of a USB-C PD charger.
So, I have a choice, I can carry this widget, and, over the course of 1 hour of charging, transfer about 1/3 the of the capacity to the phone. Or, for about the same weight, I can carry a USB-C PD charger and turbo-charge it in about 5-minutes to the same amount. Hmm.
So lets do a bit of a trial, to see if this modest (and free) device holds up to its 1200mAh claim. I'm thinking it will, the cell in it new would have been ~2000-~3000 mAh, so used @ 1200mAh sounds ok (some losses will occur in the 3.6V - 5.0V boost circuit too).
Bust out the 'meter' and some resistors (and a fan). Here we are just after plugging in, 5.0V output @ 1.05A. Good!
And here we are 1:13:29 later, just before it shuts off. 1208mAh have been transferred to the device under charge. OK, story checks out, they spec'd it accurately.
But, would I carry this? No way. Its not longer good enough. If it was a ~20K mAh bank w/ USB-C PD then maybe. But that would be outside the $1 target cost to make a marketing give-away feasible.
So, marketers of the online universe... Save your $, and save the landfill, these are no longer 'cool' and no longer useful.