Indeed, I bought two PD power banks and one will charge annafi (about two charges) but the nicer one gets confused and tries to use it as a power source running it down.
The one that works is no longer on Amazon UK so no link
But was a
1 X Usb Type C Power Bank, Puridea QC 3.0 Quick Charger + 18W PD 20000 mAh Portable Charger with Power LCD Display (18W Faster Charger Input,QC 3.0 USB Po
Sold by Baokudi
£18.99
So Watt Hours equals 3.7x20=74Wh allowing for no losses and the battery actually having that capacity.
The one that does not work
http://amzn.eu/d/9rCVE0G so don't get one of these.
The Anafi battery specs
SMART BATTERY
- Type: High density LiPo (2 cells)
- Capacity: 2,700mAh
- Flight time per charge: 25min
- Charging port: USB-C
- Weight: 126g
- Voltage: 7.6V
- Max charging power: 24W
So it is a 20.52 Watt Hour battery (VxA)
Charging with a "real" solar panel system connected to a regulator with USB output should be possible but not from the joke solar panels on the side of a power bank. A lot of power bank sellers also greatly exaggerated the capacity of the battery fitted.