>Powerbank reviews
I got two powerbanks for two different usecases; a Sharge Flow Mini 2 (5000 mAh) and a Voltme 10000 mAh one. The sharge is more compact and better suited for a quick top-up or carrying in a jacket, while the Voltme is for when I'd go on a hike and have to recharge my phone a few times over multiple days.
Since so many people just review powerbanks based on vibes, I actually took measurements, using a HiDance USB-C tester.
Note that I usually don't have a need for this much power, so the discharges happened in parts over multiple days. Some losses are expected due to that, so consider my measurements a reasonably close lower bound.

>HiDance USB-C Tester (4.02€)
I can't vouch for how accurate it is, but it seems fine, works great for measuring power, remembers measurements even after unplugging.

>Sharge Flow Mini 2 (16.87€)
5,000 mAh advertised capacity.
Input energy to charge to full: 19,428 mWh
Output energy from full: 15,135 mWh
@ 3.7V li-ion cell voltage, that's 5,250.81 mAh
@ 5V (output voltage) that's 3,885.6 mAh
Efficiency is ~78%

>Voltme 10,000 mAh (10.71€) (coins discount)
10,000 mAh advertised capacity
Input energy to charge to full: 42,191 mWh
Output energy from full: 33798 mWh (average of 2 measurements)
@ 3.7V li-ion cell voltage that's 9,134 mAh
@ 5V output voltage that's 6,760 mAh
Efficiency is ~80%


Frankly, I am happy with both, they both have good use-cases. The Sharge is pleasantly honest with its capacity, very compact and easy to carry. It also has a built-in share plug, which is nice for when you have no cables with you. It's great for urban daily use.
The volte slightly lied about the capacity, but it's really close and given that I got it for an insanely cheap price, I expected much worse to be honest. It's still not too bulky and heavy, it seems well made, it's got both a USB-A and USB-C plug as well as a built in USB-C cable, so if you have cables you can share with it too.
Overall, two great purchases.